Anaphase Definition
Anaphase is a stage during eukaryotic cell division in which the chromosomes are segregated to opposite poles of the cell. The stage before anaphase, metaphase, the chromosomes are pulled to the metaphase plate, in the middle of the cell. Although the chromosomes were heavily condensed in the start of cell division, they continue to condense through anaphase. Anaphase starts after the cell passes the spindle formation checkpoint, which allows chromosomes or chromatids to separate. As the microtubules shorten that connect the chromosomes to the centrosomes, the chromosomes are pulled toward the centrosome until they form a semi-circle around it. In the next stage of cell division, telophase, the cell reforms the nucleus and prepares to divide.
The spindle formation checkpoint occurs before anaphase can start. This cellular mechanism insures that all chromosomes are connected to microtubules and are aligned on the metaphase plate. Once this step occurs, the cell releases a signal that creates anaphase promoting complex or APC, a substance which will act to start the process of dividing homologous chromosomes or sister chromatids, depending on which cell cycle is taking place. The APC, as seen in the graphic below, will degrade securin, an inhibitory molecule that stops the action of separase. Once separase is released, it can act on the cohesins that hold chromatids together. Cohesins are macromolecules that consists of multiple proteins. When these proteins are broken down by separase, the chromatids come apart. In the first division of meiosis, homologous chromosomes are held together by cohesins that break down during anaphase I.
The microtubules stay attached to the kinetochore after the cohesins are broken apart. The kinetochore microtubules then shrink towards the centrosomes (not pictured), which pulls the chromosomes apart. Non-kinetochore microtubules grow in the opposite direction, expanding the cell and further separating the chromatids. Conventionally, sister chromatids are called sister chromosomes once they separate, as they contain the same information and will function independently in their new cells. After the chromosomes have been fully separated, a nuclear envelope will form and the cytoplasm will be divided in the final steps of cell division.
Anaphase in Mitosis
Mitosis is the process cells use to make exact copies of themselves. Through mitosis, two new daughter cells are created from a single parent, each identical to the parent. Before mitosis, the chromosomes containing DNA are replicated and the replicated sister chromatids remain attached. Before anaphase, the chromosomes are condensed, the spindle fibers form out of microtubules, and the chromosomes align on the metaphase plate. The sister chromatids begin to separate at the onset of anaphase, when separase begins to break the cohesin that binds them together. Anaphase ends when telophase and cytokinesis begin, as the nuclear envelope reforms and the chromosomes begin to unwind. Once they are loose and the cells have been divided, they can again start to function on their own. This marks the end of cell division and the beginning of interphase.
Anaphase in Meiosis
Anaphase I
Meiosis consists of two consecutive cell divisions, with no DNA replicated in between. This means that a diploid organisms, containing two alleles for each gene, will be reduced to a haploid organism, with only one allele at each gene. These alleles are separated during anaphase I. Before meiosis, the DNA is duplicated, again producing sister chromatids bound together as single chromosomes. These chromosomes have homologous pairs, which contain the other alleles for the genes on the chromosome. These chromosomes are also duplicated into sister chromatids. During meiosis I, the homologous chromosomes are separated.
The homologous chromosomes become bound together during prophase I of meiosis, by similar molecules of cohesin that bind sister chromatids. As the meiotic spindle sets up during metaphase I, the cell ensures that each homologous pair becomes attached to microtubules from each side of the cell. These microtubules then pull against each other to move the homologous pairs to the metaphase plate. During the time the pairs are bonded, they can exchange genetic information in a process called recombination. When the homologous pairs are separated during anaphase I, the DNA variations become destined for different cells, ensuring variability in a population’s genetics.
Anaphase II
Meiosis is completed with a second division of each new daughter cell. The same stages occur, this time in a fashion more similar to mitosis. The chromosomes, still made of sister chromatids, align on the metaphase plate, and must complete a checkpoint to proceed to anaphase II. At the onset of anaphase II, the sister chromatids are separated when the cohesin binding them is released. The copies of the chromosome are then separated to their final destination. These new cell will give rise to gametes which can fertilize a gamete of the opposite sex to produce a new offspring.
If the cellular checkpoints leading to anaphase I or anaphase II fail, the end result will be too many copies of a chromosome (or many) in the final gamete. This condition, known as nondisjunction, may result in fatal birth defects and other symptoms in many sexually reproducing animals. In humans these conditions include Down Syndrome, Edwards Syndrome, Klinefelter Syndrome and Turner’s syndrome. These syndromes have a variety of developmental symptoms that create phenotypes that are different from the average.
- Nondisjunction – A condition caused by the failure of chromosomes to separate during either division of meiosis.
- Cytokinesis – The final stage in mitosis or meiosis, in which the cell membrane divides.
- Anaphase Promoting Complex – The system of proteins, coenzymes, and other molecules that enable separase to degrade cohesin molecules, leading to separation of chromosomes.
- Cohesin – The protein molecules that bind sister chromatids or homologous chromosomes together.
Quiz
1. A cell is undergoing mitosis. The chromosomes have separated and are moving to their new nuclei, but nuclear envelopes have not reformed. What stage is the cell in?
A. Prophase
B. Anaphase
C. Telophase
Answer to Question #1
B is correct. This cell is in anaphase. Telophase is marked by the reformation of the nuclear envelopes and the further division of the organelles and cytosol. Telophase is completed when cytokinesis cleave the cell into two. The line between anaphase and telophase is gray, but the nuclear envelope begins forming at the onset of telophase. The chromosomes may still be moving to their final positions as this happens.
2. Anaphase happens incredibly quickly. The entire process accounts for only 1% of a cell cycle. Why are the chromosomes not ripped apart during this violent movement?
A. The condensed DNA is more protected from harm
B. Long segments of DNA called telomeres protect the ends of the DNA
C. Both A and B
Answer to Question #2
C is correct. DNA is protected by a number of mechanisms, only two of which are telomeres and the ability to condense. The spindle fibers also protect DNA, as they provide a clear path in one direction for the chromosome to travel on. The DNA is also quickly surrounded by a nuclear envelope after anaphase, which protects it for the rest of cell division.
3. Yeast are single-celled eukaryotic organisms. A yeast is going through mitosis, and is currently in anaphase. How many organisms are present now, and how many will there be after cytokinesis?
A. 2 ; 4
B. 1 ; 1
C. 1 ; 2
Answer to Question #3
C is correct. Yeast can sometimes reproduce sexually, but this is an example of how they reproduce asexually. Thus, after the cell divides, there are two organisms present when only one was present during anaphase. This is true of any single-celled organism that undergoes mitosis. The separation of the two cells is the dividing line between one organism and two, as the cell membrane physically separates the contents of each cell from the other. This means the organisms are theoretically independent, although they may still interact.
FAQs
What is anaphase in mitosis and meiosis? ›
Anaphase is the fourth phase of mitosis, the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells.
What is the anaphase stage of meiosis? ›Anaphase I begins when homologous chromosomes separate. The nuclear envelope reforms and nucleoli reappear. The chromosomes coil up, the nuclear membrane begins to disintegrate, and the centrosomes begin moving apart. Spindle fibers form and sister chromatids align to the equator of the cell.
What are the stages of anaphase in mitosis? ›Anaphase consists of two phases, anaphase A and B. During anaphase A, the chromosomes move to the poles and kinetochore fiber microtubules shorten; during anaphase B, the spindle poles move apart as interpolar microtubules elongate and slide past one another.
What is anaphase in short answer? ›Anaphase is a mitotic stage in which the chromosomes split and the sister chromatids move towards the opposite poles of the cell. The microtubules connecting the chromosomes shorten and the chromatids are pulled towards the centrosome.
What is one difference between mitosis and meiosis during anaphase? ›The cleavage of the centromere is taken place in Anaphase of Mitosis, whereas it does not occur in Anaphase I of meiosis.
How does the anaphase stage differ in the two phases of meiosis? ›Meiosis I is reductional division and meiosis II is equational division. In anaphase I homologous chromosomes separate; in anaphase II, sister chromatids separate.
What is anaphase 2 in meiosis? ›Anaphase II: During anaphase II, the centromere splits, freeing the sister chromatids from each other. At this point, spindle fibers begin to shorten, pulling the newly-separated sister chromatids towards opposite ends of the cell.
What happens after anaphase in meiosis? ›Directly after anaphase is telophase. During telophase the spindle fibers that were moving the chromatids disappear, and new nuclear envelopes form around each set of chromatids, leaving two complete and separate nucleii, one at each pole of the cell.
Why is anaphase important in mitosis? ›Anaphase is a very important stage of cell division. It ensures that duplicated chromosomes, or sister chromatids, separate into two equal sets. This separation of chromosomes is called disjunction. Each set of chromosomes will become part of a new cell.
Where does anaphase occur in mitosis? ›Mitotic anaphase: After the mitotic metaphase (when all the chromosomes align at the metaphase plate and microtubules attach to the kinetochores), the succeeding phase is anaphase wherein the chromosomes would now move towards the poles of the spindle.
How long is anaphase in mitosis? ›
We find that in a 24-hour period, the cells we observed spend 1000.2 minutes in interphase, 180 minutes in prophase, 128.2 minutes in metaphase, 77.8 minutes in anaphase, and 51.8 minutes in telophase.
What are the stages of mitosis anaphase and prophase? ›Mitosis steps consist of prophase, metaphase, anaphase, and telophase; the cell undergoes nucleus division and split into two identical daughter cells. The stages of mitosis occur in sequence with specific events in each one.
What is anaphase and example? ›Anaphase (from Ancient Greek ἀνα- (ana-) 'back, backward', and φάσις (phásis) 'appearance') is the stage of mitosis after the process of metaphase, when replicated chromosomes are split and the newly-copied chromosomes (daughter chromatids) are moved to opposite poles of the cell.
Which of the following would be the best definition of anaphase? ›Which of the following would be the best definition of Anaphase? The centromeres of the chromosomes split apart and each chromatid becomes it's own chromosome.
What happens during anaphase of mitosis quizlet? ›What happens during Anaphase? The spindle fibers SPLIT APART the sister chromatids and move them to opposite ends of the cell, equally dividing the genetic material.
What's the difference between anaphase and metaphase in meiosis? ›In metaphase (a), the microtubules of the spindle (white) have attached and the chromosomes have lined up on the metaphase plate. During anaphase (b), the sister chromatids are pulled apart and move toward opposite poles of the cell.
What is the main event of anaphase? ›During anaphase, the sister chromatids separate and begin to migrate to opposite poles of the cell, and a cleavage furrow begins to develop.
What is a major difference between anaphase I of meiosis and the anaphase of mitosis quizlet? ›How does anaphase I of meiosis differ from anaphase of mitosis? In anaphase 1 of meiosis, homologous chromosomes separate and move towards opposite poles, while the sister chromatids stay together. In anaphase of mitosis, sister chromatids separate and move towards opposite poles.
What event occurs in both anaphase of mitosis and meiosis? ›The event that occurs in both anaphase of mitosis and anaphase II of meiosis is the separation of sister chromatids. Sister chromatids are duplicated copies of the chromosomes.
What is the difference between anaphase 1 of meiosis 1 and anaphase 2 of meiosis 2? ›During meiotic division, haploid gametes are produced from diploid germ cells. The main difference between anaphase 1 and 2 is that homologous chromosomes are separated during anaphase 1 whereas sister chromatids are separated during anaphase 2.
Does anaphase occur in meiosis 2? ›
Anaphase II is the third stage in meiosis II. It is the stage after metaphase II, which is that phase wherein the chromosomes are at the equatorial plane and spindle fibers are attached to the kinetochores.
What is the significance of anaphase 1? ›Anaphase I
This separation means that each of the daughter cells that results from meiosis I will have half the number of chromosomes of the original parent cell after interphase. Also, the sister chromatids in each chromosome still remain connected. As a result, each chromosome maintains its X-shaped structure.
Anaphase is a sub-process of mitosis and meiosis processes of cell division. Anaphase is the third stage of both the processes and is concerned with the division and distribution of cell materials. This process precedes the telophase of mitosis and meiosis while it supersedes the metaphase in both.
Which cells are anaphase stage? ›Anaphase is a stage during eukaryotic cell division in which the chromosomes are segregated to opposite poles of the cell.
What are the stages of meiosis? ›There are six stages within each of the divisions, namely prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis.
What are stages of mitosis and meiosis? ›Meiosis and mitosis both have a prophase, metaphase, anaphase, telophase and cytokinesis.
What is anaphase quizlet? ›Anaphase. The stage of meiotic or mitotic cell division in which the chromosomes move away from one another to opposite poles of the spindle.
Is anaphase 2 mitosis or meiosis? ›Meiosis II
Anaphase II: The chromatids split at the centromere and migrate along the spindle fibers to opposite poles. Telophase II: The cells pinch in the center and divide again. The final outcome is four cells, each with half of the genetic material found in the original.
During anaphase, the sister chromatids are separated simultaneously at their centromeres. The separated chromosomes are then pulled by the spindle to opposite poles of the cell. Anaphase ensures that each daughter cell receives an identical set of chromosomes.
Why is it called anaphase? ›Anaphase (from Ancient Greek ἀνα- (ana-) 'back, backward', and φάσις (phásis) 'appearance') is the stage of mitosis after the process of metaphase, when replicated chromosomes are split and the newly-copied chromosomes (daughter chromatids) are moved to opposite poles of the cell.
What happens in anaphase 1 and 2 of meiosis? ›
With meiosis, two rounds of anaphase occur. During anaphase 1, homologous chromosomes separate and move to opposite ends of the cell. With anaphase 2, the sister chromatids separate in much the same manner as mitotic anaphase.