Information

11.12: Mendel’s Experiments and Heredity - Biology

11.12: Mendel’s Experiments and Heredity - Biology


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Learning Objectives

Describe Mendel’s study of garden peas and hereditary

Genetics is the study of heredity. Johann Gregor Mendel set the framework for genetics long before chromosomes or genes had been identified, at a time when meiosis was not well understood. Mendel selected a simple biological system and conducted methodical, quantitative analyses using large sample sizes. Because of Mendel’s work, the fundamental principles of heredity were revealed. We now know that genes, carried on chromosomes, are the basic functional units of heredity with the capability to be replicated, expressed, or mutated. Today, the postulates put forth by Mendel form the basis of classical, or Mendelian, genetics. Not all genes are transmitted from parents to offspring according to Mendelian genetics, but Mendel’s experiments serve as an excellent starting point for thinking about inheritance.

Mendel’s Experiments and the Laws of Probability

Johann Gregor Mendel (1822–1884) (Figure 2) was a lifelong learner, teacher, scientist, and man of faith. As a young adult, he joined the Augustinian Abbey of St. Thomas in Brno in what is now the Czech Republic. Supported by the monastery, he taught physics, botany, and natural science courses at the secondary and university levels. In 1856, he began a decade-long research pursuit involving inheritance patterns in honeybees and plants, ultimately settling on pea plants as his primary model system (a system with convenient characteristics used to study a specific biological phenomenon to be applied to other systems). In 1865, Mendel presented the results of his experiments with nearly 30,000 pea plants to the local Natural History Society. He demonstrated that traits are transmitted faithfully from parents to offspring independently of other traits and in dominant and recessive patterns. In 1866, he published his work, Experiments in Plant Hybridization, in the proceedings of the Natural History Society of Brünn.

Mendel’s work went virtually unnoticed by the scientific community that believed, incorrectly, that the process of inheritance involved a blending of parental traits that produced an intermediate physical appearance in offspring; this hypothetical process appeared to be correct because of what we know now as continuous variation. Continuous variation results from the action of many genes to determine a characteristic like human height. Offspring appear to be a “blend” of their parents’ traits when we look at characteristics that exhibit continuous variation. The blending theory of inheritance asserted that the original parental traits were lost or absorbed by the blending in the offspring, but we now know that this is not the case. Mendel was the first researcher to see it. Instead of continuous characteristics, Mendel worked with traits that were inherited in distinct classes (specifically, violet versus white flowers); this is referred to as discontinuous variation. Mendel’s choice of these kinds of traits allowed him to see experimentally that the traits were not blended in the offspring, nor were they absorbed, but rather that they kept their distinctness and could be passed on. In 1868, Mendel became abbot of the monastery and exchanged his scientific pursuits for his pastoral duties. He was not recognized for his extraordinary scientific contributions during his lifetime. In fact, it was not until 1900 that his work was rediscovered, reproduced, and revitalized by scientists on the brink of discovering the chromosomal basis of heredity.

Mendel’s Model System

Mendel’s seminal work was accomplished using the garden pea, Pisum sativum, to study inheritance. This species naturally self-fertilizes, such that pollen encounters ova within individual flowers. The flower petals remain sealed tightly until after pollination, preventing pollination from other plants. The result is highly inbred, or “true-breeding,” pea plants. These are plants that always produce offspring that look like the parent. By experimenting with true-breeding pea plants, Mendel avoided the appearance of unexpected traits in offspring that might occur if the plants were not true breeding. The garden pea also grows to maturity within one season, meaning that several generations could be evaluated over a relatively short time. Finally, large quantities of garden peas could be cultivated simultaneously, allowing Mendel to conclude that his results did not come about simply by chance.

Mendelian Crosses

Mendel performed hybridizations, which involve mating two true-breeding individuals that have different traits. In the pea, which is naturally self-pollinating, this is done by manually transferring pollen from the anther of a mature pea plant of one variety to the stigma of a separate mature pea plant of the second variety. In plants, pollen carries the male gametes (sperm) to the stigma, a sticky organ that traps pollen and allows the sperm to move down the pistil to the female gametes (ova) below. To prevent the pea plant that was receiving pollen from self-fertilizing and confounding his results, Mendel painstakingly removed all of the anthers from the plant’s flowers before they had a chance to mature.

Plants used in first-generation crosses were called P0, or parental generation one, plants (Figure 3). Mendel collected the seeds belonging to the P0 plants that resulted from each cross and grew them the following season. These offspring were called the F1, or the first filial (filial = offspring, daughter or son), generation. Once Mendel examined the characteristics in the F1 generation of plants, he allowed them to self-fertilize naturally. He then collected and grew the seeds from the F1 plants to produce the F2, or second filial, generation. Mendel’s experiments extended beyond the F2 generation to the F3 and F4generations, and so on, but it was the ratio of characteristics in the P0−F1−F2 generations that were the most intriguing and became the basis for Mendel’s postulates.

Garden Pea Characteristics Revealed the Basics of Heredity

In his 1865 publication, Mendel reported the results of his crosses involving seven different characteristics, each with two contrasting traits. A trait is defined as a variation in the physical appearance of a heritable characteristic. The characteristics included plant height, seed texture, seed color, flower color, pea pod size, pea pod color, and flower position. For the characteristic of flower color, for example, the two contrasting traits were white versus violet. To fully examine each characteristic, Mendel generated large numbers of F1 and F2 plants, reporting results from 19,959 F2 plants alone. His findings were consistent.

What results did Mendel find in his crosses for flower color? First, Mendel confirmed that he had plants that bred true for white or violet flower color. Regardless of how many generations Mendel examined, all self-crossed offspring of parents with white flowers had white flowers, and all self-crossed offspring of parents with violet flowers had violet flowers. In addition, Mendel confirmed that, other than flower color, the pea plants were physically identical.

Once these validations were complete, Mendel applied the pollen from a plant with violet flowers to the stigma of a plant with white flowers. After gathering and sowing the seeds that resulted from this cross, Mendel found that 100 percent of the F1 hybrid generation had violet flowers. Conventional wisdom at that time would have predicted the hybrid flowers to be pale violet or for hybrid plants to have equal numbers of white and violet flowers. In other words, the contrasting parental traits were expected to blend in the offspring. Instead, Mendel’s results demonstrated that the white flower trait in the F1 generation had completely disappeared.

Importantly, Mendel did not stop his experimentation there. He allowed the F1 plants to self-fertilize and found that, of F2-generation plants, 705 had violet flowers and 224 had white flowers. This was a ratio of 3.15 violet flowers per one white flower, or approximately 3:1. When Mendel transferred pollen from a plant with violet flowers to the stigma of a plant with white flowers and vice versa, he obtained about the same ratio regardless of which parent, male or female, contributed which trait. This is called a reciprocal cross—a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross. For the other six characteristics Mendel examined, the F1 and F2 generations behaved in the same way as they had for flower color. One of the two traits would disappear completely from the F1 generation only to reappear in the F2 generation at a ratio of approximately 3:1 (Table 1).

Table 1. The Results of Mendel’s Garden Pea Hybridizations
CharacteristicContrasting P0 TraitsF1 Offspring TraitsF2 Offspring TraitsF2 Trait Ratios
Flower colorViolet vs. white100 percent violet
  • 705 violet
  • 224 white
3.15:1
Flower positionAxial vs. terminal100 percent axial
  • 651 axial
  • 207 terminal
3.14:1
Plant heightTall vs. dwarf100 percent tall
  • 787 tall
  • 277 dwarf
2.84:1
Seed textureRound vs. wrinkled100 percent round
  • 5,474 round
  • 1,850 wrinkled
2.96:1
Seed colorYellow vs. green100 percent yellow
  • 6,022 yellow
  • 2,001 green
3.01:1
Pea pod textureInflated vs. constricted100 percent inflated
  • 882 inflated
  • 299 constricted
2.95:1
Pea pod colorGreen vs. yellow100 percent green
  • 428 green
  • 152 yellow
2.82:1

Upon compiling his results for many thousands of plants, Mendel concluded that the characteristics could be divided into expressed and latent traits. He called these, respectively, dominant and recessive traits. Dominant traits are those that are inherited unchanged in a hybridization. Recessive traits become latent, or disappear, in the offspring of a hybridization. The recessive trait does, however, reappear in the progeny of the hybrid offspring. An example of a dominant trait is the violet-flower trait. For this same characteristic (flower color), white-colored flowers are a recessive trait. The fact that the recessive trait reappeared in the F2 generation meant that the traits remained separate (not blended) in the plants of the F1 generation. Mendel also proposed that plants possessed two copies of the trait for the flower-color characteristic, and that each parent transmitted one of its two copies to its offspring, where they came together. Moreover, the physical observation of a dominant trait could mean that the genetic composition of the organism included two dominant versions of the characteristic or that it included one dominant and one recessive version. Conversely, the observation of a recessive trait meant that the organism lacked any dominant versions of this characteristic.

Learning Objectives

Working with garden pea plants, Mendel found that crosses between parents that differed by one trait produced F1 offspring that all expressed the traits of one parent. Observable traits are referred to as dominant, and non-expressed traits are described as recessive. When the offspring in Mendel’s experiment were self-crossed, the F2 offspring exhibited the dominant trait or the recessive trait in a 3:1 ratio, confirming that the recessive trait had been transmitted faithfully from the original P0 parent. Reciprocal crosses generated identical F1 and F2 offspring ratios. By examining large sample sizes, Mendel showed that his crosses behaved reproducibly according to the laws of probability, and that the traits were inherited as independent events.


Chapter 12 Mendels Experiments and Heredity General Biology

Chapter 12: Mendel’s Experiments and Heredity General Biology I BSC 2010 Dr. Capers Caption: Pea Plant (c)Wikipedia, Public domain Download for free at https: //cnx. org/contents/GFy_h 8 [email protected] 114: O 2 l. [email protected]/Introduction Open. Stax Biology - https: //openstax. org/details/books/biology, Power. Point made by Dr. Capers - www. jcapers-irsc. weebly. com

• Johann Gregor Mendel is considered the father of genetics. • Mendel selected a simple biological system and conducted methodical, quantitative analyses using large sample sizes. • Because of Mendel’s work, the fundamental principles of heredity were revealed. • We now know that genes, carried on chromosomes, are the basic functional units of heredity with the capability to be replicated, expressed, or mutated. • Mendels ideas form the basis of classical, or Mendelian, genetics. Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61

• It was once thought that parental traits were blended in offspring • Mendel’s choice of these traits allowed him to see experimentally that traits were not blended in offspring, they kept their distinctness Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61

Gregor Mendel Studied heredity in pea plants because: 1. Pea hybrids could be produced 2. Many pea varieties were available 3. Peas are small plants and easy to grow 4. Peas can self-fertilize or be cross- fertilized Caption: Pea Plant (C)Wikipedia, Public domain 4 Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61

Mendel’s experimental method Some Terminology: • Cross-fertilize: male and female gametes from different flowers/plant used to make zygote (pea) • Self-fertilize: male and female gametes from one flower/plant used to make zygote (pea) • True-breeding: offspring produced by self fertilization look like parent (purple flower plants make more purple colored plants). 5

• Remember that homologous chromosomes are chromosomes that have the same genes (one chromosome came from mom, one came from dad) • There be different alleles (versions) of those genes • Eye color for humans, there is Brown (B) and blue (b) • An individual that has the same 2 alleles are (BB or bb) is homozygous • An individual that has 2 different alleles (Bb) is heterozygous • One allele can be dominant over the other • The dominant is a capital letter (B), the recessive is a lower case letter (b)

Mendel’s experimental method Some Terminology: • Phenotype: The observable traits expressed by an organism (white or purple flowers) • Genotype: underlying genetic makeup, consisting of both physically visible and non-expressed alleles • Homozygous: at a given gene, or locus, have two identical alleles for that gene on their homologous chromosomes. • Heterozygous: at a given gene, or locus, have two different alleles for that gene on their homologous chromosomes. 7

• Law of Independent Assortment • During meiosis, homologous chromosomes line up randomly during metaphase • This means that not all of the maternal chromosomes will line up on one side and not all of the paternal chromosomes will line up on the other • This results in various combinations of maternal/paternal chromosomes that will end up in the resulting egg or sperm cell

Gets more complicated and there are more possible gametes when looking at genes on 2 different chromosomes

Mendel’s experimental method Self-fertilize • Pollen taken from anther used to fertilize eggs in female carpel. • Zygote forms. • True-breeding = peas produced will develop into plants with white flowers Caption: Pea Plant Anatomy (c) Wikipedia, Public domain 14

Mendel’s experimental method X • Cross-fertilize: male and female gametes from different flowers/plant used to make zygote (pea) • Remove anthers from purple flower (prevent self fertilization). • Transfer pollen from purple to white flower. • Collect peas, plant them, observe flower color of the offspring generation. 15 Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61

Mendel’s experimental method Usually 3 stages: 1. Produce true-breeding strains for each trait he was studying 2. Cross-fertilize true-breeding strains having alternate forms of a trait 3. Allow the hybrid offspring to self-fertilize for several generations and count the number of offspring showing each form of the trait 16

Monohybrid crosses Monohybrid Cross: • Mono = one trait (ex: flower color) • Hybrid = 2 variations (ex: white or purple) • Monohybrid Cross: to study 2 variations of a single trait • Mendel produced true-breeding pea strains for 7 different traits • Each trait had 2 variants 17

Caption: Pea Traits (c) Wikipedia, Public domain 18 Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61

F 1 Generation: First filial generation • Offspring of 2 true-breeding parents (P generation) • All F 1 plants looked like only 1 of parents • Visible trait in F 1 is dominant • Other trait was recessive (hidden) • No blending: No intermediate colors observed (purple-ish white) True Breeding X cross-fertilization True Breeding Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61 F 1 Generation

F 2 Generation • F 2: Offspring resulting from the self-fertilization of F 1 plants • The recessive trait is seen in some F 2 plants • F 2 Generation: • 3: 1 = 3 purple to 1 white • Always found about 3: 1 ratio • 3 dominant to 1 recessive

F 2 Ratios: Phenotype and Genotype • F 2 plants ratio based on phenotype (observable characteristics) • ¾ plants showed dominant trait • ¼ plants showed the recessive trait • Ratio of 3: 1 = 3 dominant to 1 recessive • F 2 plants ratio based on genotypes (alleles responsible for phenotype) • • 1 homozygous purple dominant = PP 2 heterozygous purple dominant = Pp 1 homozygous white recessive plant = pp Genotype ratio = 1: 2: 1 25

Punnett Square • Cross purple-flowered plant with white-flowered plant • P is dominant allele – purple flowers • p is recessive allele – white flowers • True-breeding white-flowered plant is pp • Homozygous recessive • True-breeding purple-flowered plant is PP • Homozygous dominant • Pp is heterozygote purple-flowered plant 26

Punnett Square • Let’s make a Punnett Square for cross-fertilizing a true-breeding (homozygous) purple flower with a true breeding (homozygous) white flower to create F 1 generation • What is the genotype of the purple flower? (PP, Pp or pp? ) • What is the genotype of the white flower? F 1 Generation? Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61 27

Punnett Square • Let’s make a Punnett Square fertizlizing an F 1 with another F 1 Pp x Pp • What is the genotype of the F 2 purple flowers? Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61 29

Pedigree Analysis • Pedigree Analysis: track pattern of inheritance in a family • A genetic family tree • Track dominant or recessive traits or genetic diseases 32 Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61

How to read a pedigree: • Squares are male • Circles are female • Shapes filled in with color are affected/have trait 33

Autosomal Dominant Inheritance Rules: 1. Every affected person has an affected parent 2. About half of the offspring of just one affected parent are also affected 3. The phenotype occurs equally in both sexes (so not on X or Y chromosome) 4. Affected individuals have at least one dominant allele 34

Autosomal Recessive Inheritance Rules: 1. Most affected individuals do not have affected parents • Skips generations 2. Males and females equally likely to be affected 3. Carriers: healthy individuals that are heterozygous, they have one good allele and one bad allele (Aa) 1. Sometimes on a pedigree carrier boxes/circles will be half colored in Caption: Recessive (c) Wikipedia, Public domain 36

Autosomal Recessive Inheritance Rules: 1. Most affected individuals do not have affected parents • Skips generations 2. Males and females equally likely to be affected 3. Carriers: healthy individuals that are heterozygous, they have one good allele and one bad allele (Aa) Caption: Recessive Pedigree (c) Wikipedia, Public domain

Question R = round seed r = wrinkled seed • A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant. What are the genotypes of the parents? _____ x _____ • What percentage of the offspring will also be homozygous? _______ 39

Question P = purple p = white Two plants, both heterozygous for the gene that controls flower color are crossed. What percentage of their offspring will have purple flowers? _______ What percentage will have white flowers? ______ 40

Dihybrid Crosses • Dihybrid Cross: a cross between two true-breeding parents that express different traits for two characteristics • Consider the characteristics of seed color and seed texture for two pea plants, one has green, wrinkled seeds (yyrr) and another has yellow, round seeds (YYRR). • The law of segregation indicates that the gametes for the green/wrinkled plant all are yr, and the gametes for the yellow/round plant are all YR. • So, if YYRR is crossed with yyrr, • The offspring (F 1 generation) will be Yy. Rr 41

Dihybrid Cross A male rabbit with the genotype GGBB is crossed with a female rabbit with the genotype ggbb. • What is the genotype of all of the offspring? • What is the phenotype of all of the offspring? G = grey fur g = white fur B = black eyes b = red eyes 47

Dihybrid Cross A male rabbit with the genotype Gg. Bb is crossed with a female rabbit with the genotype Gg. Bb. Set up your dihybrid square. Fill it out and determine the phenotypes and proportions in the offspring. • How many out of 16 have grey fur and black eyes? ____ • How many out of 16 have grey fur and red eyes? _____ • How many out of 16 have white fur and black eyes? ____ • How many out of 16 have white fur and red eyes? _____ G = grey fur g = white fur B = black eyes b = red eyes 48

Alternatives to Dominance and Recessiveness • So far, with Mendelian Genetics, we have been discussing traits as if there were only 2 alleles for each trait AND one was dominant over the other • However, inheritance is not always this easy • Exceptions to simple Mendelian Genetics: • Multiple Alleles – there may be more than just 2 alleles for certain genes • Polygenic traits - Multiple genes might influence a phenotype • Incomplete dominance – neither allele may be dominant or recessive, resulting in new phenotype • Codominance – both alleles present are expressed equally • Epistasis – presence of one gene can effect expression of another gene (even on a different chromosome) • X-linked traits (genes on the sex chromosomes)

Multiple Alleles • Mendel: only two alleles, one dominant and one recessive exist for a given gene • However, Multiple alleles may exist at the population level such that many combinations of two alleles are observed • The most common phenotype or genotype among wild animals as the wild type (often abbreviated “+”) • All other phenotypes or genotypes are considered variants Caption: Rabbit (c) Wikipedia, Public domain

Polygenic Traits - Multiple Genes May Be Involved with Certain Phenotypes • Height in humans is a good example • There are several genes that determine one’s height • That’s why we don’t have just short people and tall people, there are people at all ranges

Incomplete Dominance Figure 12. 7 Incomplete dominance, denoting the expression of two contrasting alleles such that the individual displays an intermediate phenotype A cross between a homozygous parent with white flowers and a homozygous parent with red flowers will produce offspring with pink flowers Download for free at http: //cnx. org/contents/185 cbf 87 -c 72 e-48 f 5 -b 51 e-f 14 f 21 b 5 [email protected] 61

Examples • A man with type A blood is married to a woman with type O blood. What are ALL of the possible blood types of their children. • A man with type AB blood is married to a woman with type AB blood. What are all the possible blood types of their children? 54

Sex Chromosomes • The sex of a human is determined by the Y chromosome • Chromosomes XX = female • Chromosomes XY = male • There is an SRY gene on the Y chromosome – will induce production of testosterone • Humans have 46 total chromosomes • 22 pairs are autosomes • 1 pair of sex chromosomes Caption: XX (c) Wikipedia, Public domain Caption: XY (c) Wikipedia, Public domain 57

Sex Linkage and Human Traits and Disease • X-linked human diseases • Examples: color blindness, hemophilia, and muscular dystrophy • Because human males need to inherit only one recessive mutant X allele to be affected, X-linked disorders are disproportionately observed in males. • Females must inherit recessive X-linked alleles from both of their parents in order to express the trait • Therefore, recessive X-linked traits appear more frequently in males than females • Watch this video: https: //www. youtube. com/watch? v=h 2 xufr. HWG 3 E 58

Lethality • Occasionally, a nonfunctional allele for an essential gene can arise by mutation and be transmitted in a population as long as individuals with this allele also have a wild-type, functional copy • Depending on what life stage requires this essential gene, individuals with the nonfunctional allele might: 1. Fail to develop past fertilization 2. Die in utero 3. die later in life, but younger than average lifespan • Recessive Lethal: inheritance pattern in which an allele is only lethal in the homozygous form and in which the heterozygote may be normal or have some altered non-lethal phenotype • Examples in humans: cystic fibrosis, Tay-sachs diseases, sickle cell anemia • Dominant Lethal: an allele is lethal in both the homozygote and heterozygote • Examples in humans: Hungtinton’s disease


39. The gene SLC24A5 encodes an antiporter membrane protein that exchanges sodium for calcium (R. Ginger et al., JBC, 2007). This process has a role in the synthesis of the melanosomes that cause ski .

  • You are here:  
  • Home
  • Umbrella
  • Textbooks
  • Bio581
  • Chapter 29 The Musculoskeletal System
  • 29.3 Joints and Skeletal Movement

This text is based on Openstax Biology for AP Courses, Senior Contributing Authors Julianne Zedalis, The Bishop's School in La Jolla, CA, John Eggebrecht, Cornell University Contributing Authors Yael Avissar, Rhode Island College, Jung Choi, Georgia Institute of Technology, Jean DeSaix, University of North Carolina at Chapel Hill, Vladimir Jurukovski, Suffolk County Community College, Connie Rye, East Mississippi Community College, Robert Wise, University of Wisconsin, Oshkosh

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 Unported License, with no additional restrictions


Garden Pea Characteristics Revealed the Basics of Heredity

In his 1865 publication, Mendel reported the results of his crosses involving seven different characteristics, each with two contrasting traits. A trait is defined as a variation in the physical appearance of a heritable characteristic. The characteristics included plant height, seed texture, seed color, flower color, pea-pod size, pea-pod color, and flower position. For the characteristic of flower color, for example, the two contrasting traits were white versus violet. To fully examine each characteristic, Mendel generated large numbers of F1 and F2 plants and reported results from thousands of F2 plants.

What results did Mendel find in his crosses for flower color? First, Mendel confirmed that he was using plants that bred true for white or violet flower color. Irrespective of the number of generations that Mendel examined, all self-crossed offspring of parents with white flowers had white flowers, and all self-crossed offspring of parents with violet flowers had violet flowers. In addition, Mendel confirmed that, other than flower color, the pea plants were physically identical. This was an important check to make sure that the two varieties of pea plants only differed with respect to one trait, flower color.

Once these validations were complete, Mendel applied the pollen from a plant with violet flowers to the stigma of a plant with white flowers. After gathering and sowing the seeds that resulted from this cross, Mendel found that 100 percent of the F1 hybrid generation had violet flowers. Conventional wisdom at that time would have predicted the hybrid flowers to be pale violet or for hybrid plants to have equal numbers of white and violet flowers. In other words, the contrasting parental traits were expected to blend in the offspring. Instead, Mendel’s results demonstrated that the white flower trait had completely disappeared in the F1 generation.

Importantly, Mendel did not stop his experimentation there. He allowed the F1 plants to self-fertilize and found that 705 plants in the F2 generation had violet flowers and 224 had white flowers. This was a ratio of 3.15 violet flowers to one white flower, or approximately 3:1. When Mendel transferred pollen from a plant with violet flowers to the stigma of a plant with white flowers and vice versa, he obtained approximately the same ratio irrespective of which parent—male or female—contributed which trait. This is called a reciprocal cross —a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross. For the other six characteristics that Mendel examined, the F1 and F2 generations behaved in the same way that they behaved for flower color. One of the two traits would disappear completely from the F1 generation, only to reappear in the F2 generation at a ratio of roughly 3:1 ([Figure 3]).

Figure 3: Mendel identified seven pea plant characteristics.

Upon compiling his results for many thousands of plants, Mendel concluded that the characteristics could be divided into expressed and latent traits. He called these dominant and recessive traits, respectively. Dominant traits are those that are inherited unchanged in a hybridization. Recessive traits become latent, or disappear in the offspring of a hybridization. The recessive trait does, however, reappear in the progeny of the hybrid offspring. An example of a dominant trait is the violet-colored flower trait. For this same characteristic (flower color), white-colored flowers are a recessive trait. The fact that the recessive trait reappeared in the F2 generation meant that the traits remained separate (and were not blended) in the plants of the F1 generation. Mendel proposed that this was because the plants possessed two copies of the trait for the flower-color characteristic, and that each parent transmitted one of their two copies to their offspring, where they came together. Moreover, the physical observation of a dominant trait could mean that the genetic composition of the organism included two dominant versions of the characteristic, or that it included one dominant and one recessive version. Conversely, the observation of a recessive trait meant that the organism lacked any dominant versions of this characteristic.

For an excellent review of Mendel’s experiments and to perform your own crosses and identify patterns of inheritance, visit the Mendel’s Peas web lab.


Mendelian Crosses

Mendel performed hybridizations, which involve mating two true-breeding individuals that have different traits. In the pea, which is naturally self-pollinating, this is done by manually transferring pollen from the anther of a mature pea plant of one variety to the stigma of a separate mature pea plant of the second variety. In plants, pollen carries the male gametes (sperm) to the stigma, a sticky organ that traps pollen and allows the sperm to move down the pistil to the female gametes (ova) below. To prevent the pea plant that was receiving pollen from self-fertilizing and confounding his results, Mendel painstakingly removed all of the anthers from the plant’s flowers before they had a chance to mature.

Plants used in first-generation crosses were called P0, or parental generation one, plants (Figure 3). Mendel collected the seeds belonging to the P0 plants that resulted from each cross and grew them the following season. These offspring were called the F1, or the first filial (filial = offspring, daughter or son), generation. Once Mendel examined the characteristics in the F1 generation of plants, he allowed them to self-fertilize naturally. He then collected and grew the seeds from the F1 plants to produce the F2, or second filial, generation. Mendel’s experiments extended beyond the F2 generation to the F3 and F4generations, and so on, but it was the ratio of characteristics in the P0−F1−F2 generations that were the most intriguing and became the basis for Mendel’s postulates.

Figure 3. In one of his experiments on inheritance patterns, Mendel crossed plants that were true-breeding for violet flower color with plants true-breeding for white flower color (the P0 generation). The resulting hybrids in the F1 generation all had violet flowers. In the F2 generation, approximately three quarters of the plants had violet flowers, and one quarter had white flowers.


12.1 | Mendel’s Experiments and the Laws of Probability

By the end of this section, you will be able to:

  • Describe the scientific reasons for the success of Mendel’s experimental work
  • Describe the expected outcomes of monohybrid crosses involving dominant and recessive alleles
  • Apply the sum and product rules to calculate probabilities
Figure 12.2Johann Gregor Mendel is considered the father of genetics.

Johann Gregor Mendel (1822–1884) (Figure 12.2) was a lifelong learner, teacher, scientist, and man of faith. As a young adult, he joined the Augustinian Abbey of St. Thomas in Brno in what is now the Czech Republic. Supported by the monastery, he taught physics, botany, and natural science courses at the secondary and university levels. In 1856, he began a decade-long research pursuit involving inheritance patterns in honeybees and plants, ultimately settling on pea plants as his primary model system (a system with convenient characteristics used to study a specific biological phenomenon to be applied to other systems). In 1865, Mendel presented the results of his experiments with nearly 30,000 pea plants to the local Natural History Society. He demonstrated that traits are transmitted faithfully from parents to offspring independently of other traits and in dominant and recessive patterns. In 1866, he published his work, Experiments in Plant Hybridization, [1] in the proceedings of the Natural History Society of Brünn.

Mendel’s work went virtually unnoticed by the scientific community that believed, incorrectly, that the process of inheritance involved a blending of parental traits that produced an intermediate physical appearance in offspring this hypothetical process appeared to be correct because of what we know now as continuous variation. Continuous variation results from the action of many genes to determine a characteristic like human height. Offspring appear to be a “blend” of their parents’ traits when we look at characteristics that exhibit continuous variation. The blending theory of inheritance asserted that the original parental traits were lost or absorbed by the blending in the offspring, but we now know that this is not the case. Mendel was the first researcher to see it. Instead of continuous characteristics, Mendel worked with traits that were inherited in distinct classes (specifically, violet versus white flowers) this is referred to as discontinuous variation. Mendel’s choice of these kinds of traits allowed him to see experimentally that the traits were not blended in the offspring, nor were they absorbed, but rather that they kept their distinctness and could be passed on. In 1868, Mendel became abbot of the monastery and exchanged his scientific pursuits for his pastoral duties. He was not recognized for his extraordinary scientific contributions during his lifetime. In fact, it was not until 1900 that his work was rediscovered, reproduced, and revitalized by scientists on the brink of discovering the chromosomal basis of heredity.

Mendel’s Model System

Mendel’s seminal work was accomplished using the garden pea, Pisum sativum, to study inheritance. This species naturally self-fertilizes, such that pollen encounters ova within individual flowers. The flower petals remain sealed tightly until after pollination, preventing pollination from other plants. The result is highly inbred, or “true-breeding,” pea plants. These are plants that always produce offspring that look like the parent. By experimenting with true-breeding pea plants, Mendel avoided the appearance of unexpected traits in offspring that might occur if the plants were not true breeding. The garden pea also grows to maturity within one season, meaning that several generations could be evaluated over a relatively short time. Finally, large quantities of garden peas could be cultivated simultaneously, allowing Mendel to conclude that his results did not come about simply by chance.

Mendelian Crosses

Mendel performed hybridizations, which involve mating two true-breeding individuals that have different traits. In the pea, which is naturally self-pollinating, this is done by manually transferring pollen from the anther of a mature pea plant of one variety to the stigma of a separate mature pea plant of the second variety. In plants, pollen carries the male gametes (sperm) to the stigma, a sticky organ that traps pollen and allows the sperm to move down the pistil to the female gametes (ova) below. To prevent the pea plant that was receiving pollen from self-fertilizing and confounding his results, Mendel painstakingly removed all of the anthers from the plant’s flowers before they had a chance to mature.

Plants used in first-generation crosses were called P0, or parental generation one, plants (Figure). Mendel collected the seeds belonging to the P0 plants that resulted from each cross and grew them the following season. These offspring were called the F1, or the first filial (filial = offspring, daughter or son), generation. Once Mendel examined the characteristics in the F1 generation of plants, he allowed them to self-fertilize naturally. He then collected and grew the seeds from the F1 plants to produce the F2, or second filial, generation. Mendel’s experiments extended beyond the F2 generation to the F3 and F4 generations, and so on, but it was the ratio of characteristics in the P0−F1−F2 generations that were the most intriguing and became the basis for Mendel’s postulates.

Figure12.3 In one of his experiments on inheritance patterns, Mendel crossed plants that were true-breeding for violet flower color with plants true-breeding for white flower color (the P generation). The resulting hybrids in the F1 generation all had violet flowers. In the F2 generation, approximately three quarters of the plants had violet flowers, and one quarter had white flowers.

Garden Pea Characteristics Revealed the Basics of Heredity

In his 1865 publication, Mendel reported the results of his crosses involving seven different characteristics, each with two contrasting traits. A trait is defined as a variation in the physical appearance of a heritable characteristic. The characteristics included plant height, seed texture, seed color, flower color, pea pod size, pea pod color, and flower position. For the characteristic of flower color, for example, the two contrasting traits were white versus violet. To fully examine each characteristic, Mendel generated large numbers of F1 and F2 plants, reporting results from 19,959 F2 plants alone. His findings were consistent.

What results did Mendel find in his crosses for flower color? First, Mendel confirmed that he had plants that bred true for white or violet flower color. Regardless of how many generations Mendel examined, all self-crossed offspring of parents with white flowers had white flowers, and all self-crossed offspring of parents with violet flowers had violet flowers. In addition, Mendel confirmed that, other than flower color, the pea plants were physically identical.

Once these validations were complete, Mendel applied the pollen from a plant with violet flowers to the stigma of a plant with white flowers. After gathering and sowing the seeds that resulted from this cross, Mendel found that 100 percent of the F1 hybrid generation had violet flowers. Conventional wisdom at that time would have predicted the hybrid flowers to be pale violet or for hybrid plants to have equal numbers of white and violet flowers. In other words, the contrasting parental traits were expected to blend in the offspring. Instead, Mendel’s results demonstrated that the white flower trait in the F1 generation had completely disappeared.

Importantly, Mendel did not stop his experimentation there. He allowed the F1 plants to self-fertilize and found that, of F2-generation plants, 705 had violet flowers and 224 had white flowers. This was a ratio of 3.15 violet flowers per one white flower, or approximately 3:1. When Mendel transferred pollen from a plant with violet flowers to the stigma of a plant with white flowers and vice versa, he obtained about the same ratio regardless of which parent, male or female, contributed which trait. This is called a reciprocal cross—a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross. For the other six characteristics Mendel examined, the F1 and F2 generations behaved in the same way as they had for flower color. One of the two traits would disappear completely from the F1 generation only to reappear in the F2 generation at a ratio of approximately 3:1 (Table 12.1).

Upon compiling his results for many thousands of plants, Mendel concluded that the characteristics could be divided into expressed and latent traits. He called these, respectively, dominant and recessive traits. Dominant traits are those that are inherited unchanged in a hybridization. Recessive traits become latent, or disappear, in the offspring of a hybridization. The recessive trait does, however, reappear in the progeny of the hybrid offspring. An example of a dominant trait is the violet-flower trait. For this same characteristic (flower color), white-colored flowers are a recessive trait. The fact that the recessive trait reappeared in the F2 generation meant that the traits remained separate (not blended) in the plants of the F1 generation. Mendel also proposed that plants possessed two copies of the trait for the flower-color characteristic, and that each parent transmitted one of its two copies to its offspring, where they came together. Moreover, the physical observation of a dominant trait could mean that the genetic composition of the organism included two dominant versions of the characteristic or that it included one dominant and one recessive version. Conversely, the observation of a recessive trait meant that the organism lacked any dominant versions of this characteristic.

So why did Mendel repeatedly obtain 3:1 ratios in his crosses? To understand how Mendel deduced the basic mechanisms of inheritance that lead to such ratios, we must first review the laws of probability.

Probability Basics

Probabilities are mathematical measures of likelihood. The empirical probability of an event is calculated by dividing the number of times the event occurs by the total number of opportunities for the event to occur. It is also possible to calculate theoretical probabilities by dividing the number of times that an event is expected to occur by the number of times that it could occur. Empirical probabilities come from observations, like those of Mendel. Theoretical probabilities come from knowing how the events are produced and assuming that the probabilities of individual outcomes are equal. A probability of one for some event indicates that it is guaranteed to occur, whereas a probability of zero indicates that it is guaranteed not to occur. An example of a genetic event is a round seed produced by a pea plant. In his experiment, Mendel demonstrated that the probability of the event “round seed” occurring was one in the F1 offspring of true-breeding parents, one of which has round seeds and one of which has wrinkled seeds. When the F1 plants were subsequently self-crossed, the probability of any given F2 offspring having round seeds was now three out of four. In other words, in a large population of F2 offspring chosen at random, 75 percent were expected to have round seeds, whereas 25 percent were expected to have wrinkled seeds. Using large numbers of crosses, Mendel was able to calculate probabilities and use these to predict the outcomes of other crosses.

The Product Rule and Sum Rule

Mendel demonstrated that the pea-plant characteristics he studied were transmitted as discrete units from parent to offspring. As will be discussed, Mendel also determined that different characteristics, like seed color and seed texture, were transmitted independently of one another and could be considered in separate probability analyses. For instance, performing a cross between a plant with green, wrinkled seeds and a plant with yellow, round seeds still produced offspring that had a 3:1 ratio of green:yellow seeds (ignoring seed texture) and a 3:1 ratio of round:wrinkled seeds (ignoring seed color). The characteristics of color and texture did not influence each other.

The product rule of probability can be applied to this phenomenon of the independent transmission of characteristics. The product rule states that the probability of two independent events occurring together can be calculated by multiplying the individual probabilities of each event occurring alone. To demonstrate the product rule, imagine that you are rolling a six-sided die (D) and flipping a penny (P) at the same time. The die may roll any number from 1–6 (D#), whereas the penny may turn up heads (PH) or tails (PT). The outcome of rolling the die has no effect on the outcome of flipping the penny and vice versa. There are 12 possible outcomes of this action (Table 12.2), and each event is expected to occur with equal probability.

Of the 12 possible outcomes, the die has a 2/12 (or 1/6) probability of rolling a two, and the penny has a 6/12 (or 1/2) probability of coming up heads. By the product rule, the probability that you will obtain the combined outcome 2 and heads is: (D2) x (PH) = (1/6) x (1/2) or 1/12 (Table 12.3). Notice the word “and” in the description of the probability. The “and” is a signal to apply the product rule. For example, consider how the product rule is applied to the dihybrid cross: the probability of having both dominant traits in the F2 progeny is the product of the probabilities of having the dominant trait for each characteristic, as shown here:

On the other hand, the sum rule of probability is applied when considering two mutually exclusive outcomes that can come about by more than one pathway. The sum rule states that the probability of the occurrence of one event or the other event, of two mutually exclusive events, is the sum of their individual probabilities. Notice the word “or” in the description of the probability. The “or” indicates that you should apply the sum rule. In this case, let’s imagine you are flipping a penny (P) and a quarter (Q). What is the probability of one coin coming up heads and one coin coming up tails? This outcome can be achieved by two cases: the penny may be heads (PH) and the quarter may be tails (QT), or the quarter may be heads (QH) and the penny may be tails (PT). Either case fulfills the outcome. By the sum rule, we calculate the probability of obtaining one head and one tail as [(PH) × (QT)] + [(QH) × (PT)] = [(1/2) × (1/2)] + [(1/2) × (1/2)] = 1/2 (Table 12.3). You should also notice that we used the product rule to calculate the probability of PH and QT, and also the probability of PT and QH, before we summed them. Again, the sum rule can be applied to show the probability of having just one dominant trait in the F2 generation of a dihybrid cross:

To use probability laws in practice, it is necessary to work with large sample sizes because small sample sizes are prone to deviations caused by chance. The large quantities of pea plants that Mendel examined allowed him calculate the probabilities of the traits appearing in his F2 generation. As you will learn, this discovery meant that when parental traits were known, the offspring’s traits could be predicted accurately even before fertilization.


Garden Pea Characteristics Revealed the Basics of Heredity

What results did Mendel find in his crosses for flower color? First, Mendel confirmed that he had plants that bred true for white or violet flower color. Regardless of how many generations Mendel examined, all self-crossed offspring of parents with white flowers had white flowers, and all self-crossed offspring of parents with violet flowers had violet flowers. In addition, Mendel confirmed that, other than flower color, the pea plants were physically identical.

Once these validations were complete, Mendel applied the pollen from a plant with violet flowers to the stigma of a plant with white flowers. After gathering and sowing the seeds that resulted from this cross, Mendel found that 100 percent of the F1 hybrid generation had violet flowers. Conventional wisdom at that time (the blending theory) would have predicted the hybrid flowers to be pale violet or for hybrid plants to have equal numbers of white and violet flowers. In other words, the contrasting parental traits were expected to blend in the offspring. Instead, Mendel’s results demonstrated that the white flower trait in the F1 generation had completely disappeared.

Importantly, Mendel did not stop his experimentation there. He allowed the F1 plants to self-fertilize and found that, of F2-generation plants, 705 had violet flowers and 224 had white flowers. This was a ratio of 3.15 violet flowers per one white flower, or approximately 3:1. When Mendel transferred pollen from a plant with violet flowers to the stigma of a plant with white flowers and vice versa, he obtained about the same ratio regardless of which parent, male or female, contributed which trait. This is called a reciprocal cross —a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross. For the other six characteristics Mendel examined, the F1 and F2 generations behaved in the same way as they had for flower color. One of the two traits would disappear completely from the F1 generation only to reappear in the F2 generation at a ratio of approximately 3:1 (Table).

  • 705 violet
  • 224 white
  • 651 axial
  • 207 terminal
  • 787 tall
  • 277 dwarf
  • 5,474 round
  • 1,850 wrinkled
  • 6,022 yellow
  • 2,001 green
  • 882 inflated
  • 299 constricted
  • 428 green
  • 152 yellow

Upon compiling his results for many thousands of plants, Mendel concluded that the characteristics could be divided into expressed and latent traits. He called these, respectively, dominant and recessive traits. Dominant traits are those that are inherited unchanged in a hybridization. Recessive traits become latent, or disappear, in the offspring of a hybridization. The recessive trait does, however, reappear in the progeny of the hybrid offspring. An example of a dominant trait is the violet-flower trait. For this same characteristic (flower color), white-colored flowers are a recessive trait. The fact that the recessive trait reappeared in the F2 generation meant that the traits remained separate (not blended) in the plants of the F1 generation. Mendel also proposed that plants possessed two copies of the trait for the flower-color characteristic, and that each parent transmitted one of its two copies to its offspring, where they came together. Moreover, the physical observation of a dominant trait could mean that the genetic composition of the organism included two dominant versions of the characteristic or that it included one dominant and one recessive version. Conversely, the observation of a recessive trait meant that the organism lacked any dominant versions of this characteristic.

So why did Mendel repeatedly obtain 3:1 ratios in his crosses? To understand how Mendel deduced the basic mechanisms of inheritance that lead to such ratios, we must first review the laws of probability.


1. Monohybrid Cross: A pea plant that is heterozygous for the trait Tall/short allele is self-pollinated. What are the phenotypic ratios among the offspring?

2. Dihybrid Cross: In plants, round seeds is dominant to wrinkled seeds and tall is dominant to short. Show the cross between two plants that are heterozygous for both traits. What are the phenotypes of the offspring and in what proportion?

b. What if the second parent was recessive for both traits? What phenotypes would you expect in the offspring?

3. Epistatic Cross: In Labradors, the yellow coat color is epistatic. Labs can be black (dominant), brown (recessive) or yellow which is caused by a pair of recessive alleles (ee) A heterozygous black lab (BbEe) is crossed with a yellow lab (Bbee). What proportion of the offspring will be:
Black? _________ Yellow? __________ Brown? __________

4. Codominance: In cattle, coat color can be red or white. If a red cow is crossed with a white cow, the offspring is a mottled red & white – coloration farmers call “roan”. What phenotypes would you get from a cross between a roan and a white cow?

5. Blood types: If one parent has type A blood and another parent has type B blood, what are ALL the possible blood types of the children. You do not know the parents’ genotypes.

6. Sex Linked: In humans, colorblindness is a sex linked, recessive trait. If a woman who is a carrier for colorblindness marries a colorblind man, what are the chances that their children will be colorblind?

7. A hairy-stemmed (HH) purple flowered (PP) plant is crossed with one that is smooth-stemmed (hh) and white flowered (pp). Show the genotypes and phenotypes of the F1 generation.

The offspring is crossed with a double recessive test cross. The following results were obtained.

Hairy, Purple Hairy, white Smooth, Purple Smooth, white
45 5 5 45

Explain these results, include an explanation for recombination.

Determine the distance between the stem and flower alleles.

8. The follow crossover frequencies were determined from various experiments: The crossover frequency between gene A and C is 30%. The crossover frequency between B and C is 44%. How far apart are A and B? Sketch the chromosome map.

/>This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.


Eye color in humans is determined by multiple genes. Use the Eye Color Calculator to predict the eye color of children from parental eye color.

In some cases, several genes can contribute to aspects of a common phenotype without their gene products ever directly interacting. In the case of organ development, for instance, genes may be expressed sequentially, with each gene adding to the complexity and specificity of the organ. Genes may function in complementary or synergistic fashions, such that two or more genes need to be expressed simultaneously to affect a phenotype. Genes may also oppose each other, with one gene modifying the expression of another.

An example of epistasis is pigmentation in mice. The wild-type coat color, agouti (AA), is dominant to solid-colored fur (aa). However, a separate gene (C) is necessary for pigment production. A mouse with a recessive c allele at this locus is unable to produce pigment and is albino regardless of the allele present at locus A (Figure). Therefore, the genotypes AAcc, Aacc, and aacc all produce the same albino phenotype. A cross between heterozygotes for both genes (AaCc x AaCc) would generate offspring with a phenotypic ratio of 9 agouti:3 solid color:4 albino (Figure). In this case, the C gene is epistatic to the A gene.

In mice, the mottled agouti coat color (A) is dominant to a solid coloration, such as black or gray. A gene at a separate locus (C) is responsible for pigment production. The recessive c allele does not produce pigment, and a mouse with the homozygous recessive cc genotype is albino regardless of the allele present at the A locus. Thus, the C gene is epistatic to the A gene.

Epistasis can also occur when a dominant allele masks expression at a separate gene. Fruit color in summer squash is expressed in this way. Homozygous recessive expression of the W gene (ww) coupled with homozygous dominant or heterozygous expression of the Y gene (YY or Yy) generates yellow fruit, and the wwyy genotype produces green fruit. However, if a dominant copy of the W gene is present in the homozygous or heterozygous form, the summer squash will produce white fruit regardless of the Y alleles. A cross between white heterozygotes for both genes (WwYy × WwYy) would produce offspring with a phenotypic ratio of 12 white:3 yellow:1 green.

Finally, epistasis can be reciprocal such that either gene, when present in the dominant (or recessive) form, expresses the same phenotype. In the shepherd’s purse plant (Capsella bursa-pastoris), the characteristic of seed shape is controlled by two genes in a dominant epistatic relationship. When the genes A and B are both homozygous recessive (aabb), the seeds are ovoid. If the dominant allele for either of these genes is present, the result is triangular seeds. That is, every possible genotype other than aabb results in triangular seeds, and a cross between heterozygotes for both genes (AaBb x AaBb) would yield offspring with a phenotypic ratio of 15 triangular:1 ovoid.

As you work through genetics problems, keep in mind that any single characteristic that results in a phenotypic ratio that totals 16 is typical of a two-gene interaction. Recall the phenotypic inheritance pattern for Mendel’s dihybrid cross, which considered two noninteracting genes—9:3:3:1. Similarly, we would expect interacting gene pairs to also exhibit ratios expressed as 16 parts. Note that we are assuming the interacting genes are not linked they are still assorting independently into gametes.


5.10 Cultural Connection

Corn is the world’s most produced crop. Canada produces 13,000-14,000 metric Kilo tonnes of corn annually, mostly in fields in Ontario, Quebec and Manitoba. Approximately 1.5 million hectares are devoted to this crop which is critically important for both humans and livestock as a food source. Despite these high numbers of output, Canada is still only 11th on the list of world corn producers, with USA, China and Brazil claiming the top three places. How did corn become such an important part of modern agriculture?

Figure 5.10.7 Teosinte (top) is the ancestor of modern corn. Hybrids (middle) were created using artificial selection, until modern corn (bottom) was developed.

We didn’t always have corn as we know it. Modern corn is descended from a type of grass called teosinte (Figure 5.10.7) native to Mesoamerica (southern part of North America). It is estimated that Indigenous people have been harvesting corn and corn ancestors for over 9000 years. Excavations of the Xihuatoxtla Shelter in southwestern Mexico revealed our earliest evidence of domesticated corn: maize remains on tools dating back 8,700 years.

Ancient Indigenous peoples of southern Mexico developed corn from grass plants using a process we now call selective breeding , also known as artificial selection . Teosinte doesn’t resemble the corn we have today- it had only a few kernels individually encased on very hard shells, and yet today we have multiple varieties of corn with row upon row of bare kernels. This means that ancient agriculturalists among the Indigenous people of Mexico were intentionally cross-breeding strains of teosinte, and later, early maize to create plants which had more kernels, and reduced seed casings. Watch the TED Ed video in the Explore More section to see what other changes agriculturalists have made to modern-day corn.


Watch the video: 3. Mendels experiment (September 2022).


Comments:

  1. Destan

    and here there are really cool ones

  2. Chochmo

    Thanks! Useful ... .. (-___________-)

  3. Jaykell

    I apologize, but in my opinion you are wrong. I offer to discuss it. Write to me in PM, we will handle it.

  4. Delano

    Thank you very much for the information.

  5. Kohlvin

    Write emoticons more often, otherwise everything seems to be serious

  6. Arashigis

    You are not right. I can prove it. Email me at PM.



Write a message