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It seems to me that, even without replication of DNA before meiosis, the homologous pairs can still do crossover, and then be pulled to opposite poles, directly forming 2 haploid gametes.
Meiosis is the process in eukaryotic, sexually-reproducing animals that reduces the number of chromosomes in a cell before reproduction. Many organisms package these cells into gametes, such as egg and sperm. The gametes can then meet, during reproduction, and fuse to create a new zygote. Because the number of alleles was reduced during meiosis, the combination of two gametes will yield a zygote with the same number of alleles as the parents. In diploid organisms, this is two copies of each gene.
Why is it necessary for the cell to grow and duplicate its DNA before the start of meiosis? It is necessary because the DNA needs to be copied so that each new cell will receive a full set. 3. How does meiosis create four daughter cells from one parent cell?
2 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
Answer: Since the cell is dividing it needs two copies of it’s DNA. One is kept by the parent cell and the other is passed to the daughter cell….. So this process of duplicating DNA is very important, because the daugher DNA cell will likley die.
3 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
The DNA helix unwinds and the strands separate to allow the enzymes used in replication to do their work. If the DNA strand is found to be broken or damaged, the entire process stops until it is…
4 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
If a cell were to begin meiosis without duplicating its DNA, the two resulting cells would have insufficient DNA to develop properly, as there would only be one copy of each chromosome in the first cell, so as division occurs, half of the DNA needed would go to one cell, and half to the other.
5 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
Each new cell needs a DNA copy, which serves as instructions on how to function as a cell. DNA replicates before a cell divides. The replication process is semi-conservative, which means that when DNA creates a copy, half of the old strand is retained in the new strand to reduce the number of copy errors.
6 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
Why is it necessary for the cell to grow and duplicate its DNA before the start of meiosis? Name: Parker Heckman Date: It must duplicate the perfect amount It must give half During the G 1phase ,cells grow and synthesize mRNA and proteins required for DNA synthesis .Chromosomes are copied during the S phase and ,in the G 2phase ,the centinues …
7 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
Why is it necessary for the cell to grow and duplicate its DNA before the start of meiosis? To make room for the photo copied DNA and so all the cells get a copy of the DNA How does anaphase of mitosis differ from anaphase I of meiosis?
8 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
Why must cells duplicate the DNA before … into two daughter cells and they all need DNA thats why before mitosis takes place there must be a duplicate of the DNA … years before meiosis …
9 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
Before meiosis I starts, the cell goes through interphase. Just like in mitosis, the parent cell uses this time to prepare for cell division by gathering nutrients and energy and making a copy of its DNA. During the next stages of meiosis, this DNA will be switched around during genetic recombination and then divided between four haploid cells.
10 .Why is it necessary for the cell to grow and duplicate its dna before the start of meiosis?
Beside above, why is it important that the cell’s DNA is replicated before cell division? Explanation: DNA replication needs to occur because existing cells divide to produce new cells. So the DNA needs to be copied before cell division so that each new cell receives a full set of instructions!
1 .Spontaneous cell fusions amplify genetic diversity within tumors
The ability to continuously create a diverse set of new cellular features enables cancers to develop the ability to grow … by cell fusions. Why is parasexual recombination important? In its …
Published Date: 2021-01-26T10:22:00.0000000Z
|1 Meiosis (Updated)|
|Updated meiosis video. Join the Amoeba Sisters as they explore the meiosis stages with vocabulary including chromosomes, centromeres, centrioles, spindle fibers, and crossing over. Expand details to see table of contents p This video also compares meiosis with mitosis. This video has a handout here: http://www.amoebasisters.com/handouts.html …|
|Watch Video: https://www.youtube.com/watch?v=VzDMG7ke69g|
miscarriage and the most frequent genetic cause of developmental disabilities. In meiosis , DNA replication is followed by two rounds of cell division to produce…
products, and its primary adaptive function appears to be repair of DNA damages in the recipient cell . The diploid nature of chromosomes allows for genes…
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@umbra21 - They take advantage of that function in cancer cells when they grow human cells for laboratory testing.
Most of the cells used in lab testing were originally samples from cancer patients, where it was discovered that the sample just continues to grow without the DNA replication process eventually breaking down, like it does with normal cells.
I know there's one particular strain of cells that's been going since the 1960's. The woman who was the original donor of the cells is long gone, but because her DNA was faulty her cells continue to live on today.
It's a bit creepy on the one hand, but on the other hand, you're right in that it could eventually lead to humans being able to live for a very long time. umbra21 January 2, 2012
@browncoat - Well, you also have to consider that DNA replication isn't perfect. Even when you have identical twins, they often have genetic differences, which I think can skew those studies, making it even more likely that genetics is a huge factor in a lot of cases.
What I find interesting about DNA replication is that there is actually a mechanism in the process which prevents it from happening too many times. Eventually the cell is forced to stop.
When this process gets corrupted it can lead to cancer, for example, because the cells won't die when they are supposed to, to make way for other cells.
But scientists are also looking into this process to see if it can help people live longer, since part of what makes us age is that certain cells, particularly in the brain, stop replicating DNA and start to die off.
If they can one day find a way to change this, without causing cancerous growths then in theory, a person could live almost indefinitely. browncoat January 1, 2012
My friend and I were just talking today about the whole nature versus nurture debate. I tend to think that people are quite influenced by the genes they inherit from their parents.
My friend thought it was more to do with how a person is influenced as they grow up.
Actually there's quite a bit of science on my side, as there have been numerous twin studies showing that even personality has more to do with what your chromosomes look like than what kind of situation you grow up in.
Of course, you can always use extreme examples like people growing up in abusive homes and so forth to make the argument that environment causes just as much influence. It's difficult to know for sure.
14.1 | Historical Basis of Modern Understanding
By the end of this section, you will be able to:
- Explain transformation of DNA.
- Describe the key experiments that helped identify that DNA is the genetic material.
- State and explain Chargaff’s rules
Modern understandings of DNA have evolved from the discovery of nucleic acids to the development of the double-helix model. In the 1860s, Friedrich Miescher (Figure 14.2), a physician by profession, was the first person to isolate phosphate- rich chemicals from white blood cells or leukocytes. He named these chemicals (which would eventually be known as RNA and DNA) nuclein because they were isolated from the nuclei of the cells.
Figure 14.2 Friedrich Miescher (1844–1895) discovered nucleic acids.
A half century later, British bacteriologist Frederick Griffith was perhaps the first person to show that hereditary information could be transferred from one cell to another “horizontally,” rather than by descent. In 1928, he reported the first demonstration of bacterial transformation, a process in which external DNA is taken up by a cell, thereby changing morphology and physiology. He was working with Streptococcus pneumoniae, the bacterium that causes pneumonia. Griffith worked with two strains, rough (R) and smooth (S). The R strain is non-pathogenic (does not cause disease) and is called rough because its outer surface is a cell wall and lacks a capsule as a result, the cell surface appears uneven under the microscope. The S strain is pathogenic (disease-causing) and has a capsule outside its cell wall. As a result, it has a smooth appearance under the microscope. Griffith injected the live R strain into mice and they survived. In another experiment, when he injected mice with the heat-killed S strain, they also survived. In a third set of experiments, a mixture of live R strain and heat-killed S strain were injected into mice, and—to his surprise—the mice died. Upon isolating the live bacteria from the dead mouse, only the S strain of bacteria was recovered. When this isolated S strain was injected into fresh mice, the mice died. Griffith concluded that something had passed from the heat-killed S strain into the live R strain and transformed it into the pathogenic S strain, and he called this the transforming principle (Figure 11.3). These experiments are now famously known as Griffith’s transformation experiments.
Figure 14.3 Two strains of S.pneumoniae were used in Griffith’s transformation experiments. The R strain is non- pathogenic. The S strain is pathogenic and causes death. When Griffith injected a mouse with the heat-killed S strain and a live R strain, the mouse died. The S strain was recovered from the dead mouse. Thus, Griffith concluded that something had passed from the heat-killed S strain to the R strain, transforming the R strain into S strain in the process. (credit “living mouse”: modification of work by NIH credit “dead mouse”: modification of work by Sarah Marriage)
Scientists Oswald Avery, Colin MacLeod, and Maclyn McCarty (1944) were interested in exploring this transforming principle further. They isolated the S strain from the dead mice and isolated the proteins and nucleic acids, namely RNA and DNA, as these were possible candidates for the molecule of heredity. They conducted a systematic elimination study. They used enzymes that specifically degraded each component and then used each mixture separately to transform the R strain. They found that when DNA was degraded, the resulting mixture was no longer able to transform the bacteria, whereas all of the other combinations were able to transform the bacteria. This led them to conclude that DNA was the transforming principle.
Experiments conducted by Martha Chase and Alfred Hershey in 1952 provided confirmatory evidence that DNA was the genetic material and not proteins. Chase and Hershey were studying a bacteriophage, which is a virus that infects bacteria. Viruses typically have a simple structure: a protein coat, called the capsid, and a nucleic acid core that contains the genetic material, either DNA or RNA. The bacteriophage infects the host bacterial cell by attaching to its surface, and then it injects its nucleic acids inside the cell. The phage DNA makes multiple copies of itself using the host machinery, and eventually the host cell bursts, releasing a large number of bacteriophages. Hershey and Chase labeled one batch of phage with radioactive sulfur, 35 S, to label the protein coat. Another batch of phage were labeled with radioactive phosphorus, 32 P. Because phosphorous is found in DNA, but not protein, the DNA and not the protein would be tagged with radioactive phosphorus.
Each batch of phage was allowed to infect the cells separately. After infection, the phage bacterial suspension was put in a blender, which caused the phage coat to be detached from the host cell. The phage and bacterial suspension was spun down in a centrifuge. The heavier bacterial cells settled down and formed a pellet, whereas the lighter phage particles stayed in the supernatant (the liquid above the pellet). In the tube that contained phage labeled with 35 S, the supernatant contained the radioactively labeled phage, whereas no radioactivity was detected in the pellet. In the tube that contained the phage labeled with 32 P, the radioactivity was detected in the pellet that contained the heavier bacterial cells, and no radioactivity was detected in the supernatant. Hershey and Chase concluded that it was the phage DNA that was injected into the cell and carried information to produce more phage particles, thus providing evidence that DNA was the genetic material and not proteins (Figure 14.4).
Figure 14.4 In Hershey and Chase’s experiments, bacteria were infected with phage radiolabeled with either 35S, which labels protein, or 32P, which labels DNA. Only 32P entered the bacterial cells, indicating that DNA is the genetic material.
Around this same time, Austrian biochemist Erwin Chargaff examined the content of DNA in different species and found that the amounts of adenine, thymine, guanine, and cytosine were not found in equal quantities, and that it varied from species to species, but not between individuals of the same species. He found that the amount of adenine equals the amount of thymine, and the amount of cytosine equals the amount of guanine, or A = T and G = C. These are also known as Chargaff’s rules. This finding proved immensely useful when Watson and Crick were getting ready to propose their DNA double helix model, discussed in Chapter 5.
The sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles (Figure 1). Non-kinetochore microtubules elongate the cell.
In meiosis II, the connected sister chromatids remaining in the haploid cells from meiosis I will be split to form four haploid cells. The two cells produced in meiosis I go through the events of meiosis II in synchrony. Overall, meiosis II resembles the mitotic division of a haploid cell. During meiosis II, the sister chromatids are pulled apart by the spindle fibers and move toward opposite poles.Figure 1 In prometaphase I, microtubules attach to the fused kinetochores of homologous chromosomes. In anaphase I, the homologous chromosomes are separated. In prometaphase II, microtubules attach to individual kinetochores of sister chromatids. In anaphase II, the sister chromatids are separated.
Why Does DNA Need to Replicate?
DNA replicates to make copies of itself. This is an indispensable process that allows cells to divide for a living organism to grow or reproduce. Each new cell needs a DNA copy, which serves as instructions on how to function as a cell.
DNA replicates before a cell divides. The replication process is semi-conservative, which means that when DNA creates a copy, half of the old strand is retained in the new strand to reduce the number of copy errors. DNA contains the code for building an organism and making sure that the organism functions properly. For this reason, DNA is often called the blueprint of life. Its function is comparable to a builder using a blueprint to make a house. The blueprint contains all of the necessary plans and instructions for the organism. It brings the information for making a cell&rsquos proteins, which are responsible for implementing the functions of an organism and determining the organism&rsquos characteristics. After reproducing, the cell passes this crucial information to the daughter cells. DNA replication occurs in the nucleus of eukaryotes and the cytoplasm of prokaryotes. The replicating process is the same, regardless of where it takes place. Various kinds of cells replicate their DNA at different rates. Some undergo several rounds of cell division, such as those in a human&rsquos heart and brain, while other cells constantly divide, like those in the fingernails and hair.
For Students & Teachers
For Teachers Only
Heritable information provides for the continuity of life.
Explain how meiosis results in the transmission of chromosomes from one generation to the next.
Describe similarities and/or differences between the phases and outcomes of mitosis and meiosis.
Meiosis is a process that ensures the formation of haploid gamete cells in sexually reproducing diploid organisms —
- Meiosis results in daughter cells with half the number of chromosomes of the parent cell.
- Meiosis involves two rounds of a sequential series of steps (meiosis I and meiosis II).
Mitosis and meiosis are similar in the way chromosomes segregate but differ in the number of cells produced and the genetic content of the daughter cells.
The key event in prometaphase I is the attachment of the spindle fiber microtubules to the kinetochore proteins at the centromeres. Kinetochore proteins are multiprotein complexes that bind the centromeres of a chromosome to the microtubules of the mitotic spindle. Microtubules grow from centrosomes placed at opposite poles of the cell. The microtubules move toward the middle of the cell and attach to one of the two fused homologous chromosomes. The microtubules attach at each chromosomes’ kinetochores. With each member of the homologous pair attached to opposite poles of the cell, in the next phase, the microtubules can pull the homologous pair apart. A spindle fiber that has attached to a kinetochore is called a kinetochore microtubule. At the end of prometaphase I, each tetrad is attached to microtubules from both poles, with one homologous chromosome facing each pole. The homologous chromosomes are still held together at chiasmata. In addition, the nuclear membrane has broken down entirely.
Figure 4 In prometaphase I, microtubules attach to the fused kinetochores of homologous chromosomes, and the homologous chromosomes are arranged at the midpoint of the cell in metaphase I. In anaphase I, the homologous chromosomes are separated.
How DNA replication works
All living things have DNA in their nuclei. Tightly coiled into strands called chromatin, DNA contains the organism’s entire genome, or instruction manual. DNA is made of long strands of units called nucleotides. Each nucleotide contains a sugar, a phosphate group, and one of four nitrogenous bases – adenine, thymine, cytosine, or guanine.
A single DNA molecule contains two strands of nucleotides that run parallel to each other, with their bases (A, T, G, or C) hydrogen-bonded to the bases on the other strand – this forms a shape much like a ladder, the bases being the rungs. Complementary base pairing rules apply: adenine always hydrogen bonds with thymine, and cytosine always hydrogen bonds with guanine. This ladder is twisted into a helical structure.
To replicate DNA, the double-stranded molecule needs to be unwound and separated, each new strand replicated, and then each newly formed pair of strands coiled back up in nice, neat helices. The enzyme DNA helicase is responsible for uncoiling and unzipping the strands. Each newly-separated strand serves as a template for complementary nucleotides to be pulled from the surrounding nucleus and put in place as a part of the new strand. Think of unzipping a long zipper – as the zipper is undone, new zipper teeth are taken from the environment and put on the exposed zipper sides, making two complete zippers from one.
DNA polymerase III is responsible for creating the complementary strands by adding free nucleotides to the exposed bases. It, along with DNA polymerase I, also spellchecks the new strands and replaces any mistakes. Once finished, each new double-stranded DNA molecule contains one strand of the original DNA, and one strand of newly-made DNA.
The new strands are coiled back into helices and supercoiled back into chromatin and the rest of nuclear and then cell division can take place. Two copies of each chromosome now exist and one of each will go to the two new cells, ensuring that each new cell has a full set of cellular instruction for that organism.