Biology: Mitosis and Meiosis

Put the four stages of the cell cycle in the correct order: -M -S -G1 -G2

-G1 -S -G2 -M The first three stages (G1, S, and G2) are collectively known as interphase.

Put the phases of mitosis in the correct order: -Anaphase -Metaphase -Prophase -Telophase

-Prophase -Metaphase -Anaphase -Telophase and cytokinesis *Remember PMAT Meiosis has the same order except Meiosis I occurs and then Meiosis II.

What is the longest part of the cell cycle? A. Interphase B. Prophase C. Metaphase D. Anaphase

A. Interphase Interphase is the longest part of the cell cycle; even actively dividing cells spend about 90 percent of their time in interphase. Of interphase G1 takes the longest.

During cytokinesis of mitosis, what is the cleavage furrow formed from? A. Microfilaments B. Microtubules C. Intermediate Filaments D. None of the above

A. Microfilaments During cytokinesis of mitosis, the cleavage furrow formed from microfilaments, organize as a ring at the site of division between the two daughter cells. As the actin filaments within this ring contract, the ring becomes smaller, eventually pinching off the connection between the two daughter cells.

During which phase of mitosis do some microtubules form asters that anchor the centrioles to the cell membrane? A. Prophase B. Metaphase C. Anaphase D. Telophase

A. Prophase

During which phase of mitosis does the nuclear membrane dissolve, allowing the spindle fibers to contact the chromosomes? A. Prophase B. Metaphase C. Anaphase D. Telophase

A. Prophase

During which phase of mitosis does the nucleoli become less distinct, and may disappear completely? A. Prophase B. Metaphase C. Anaphase D. Telophase

A. Prophase

In which phase of mitosis does the spindle apparatus form? A. Prophase B. Metaphase C. Anaphase D. Telophase

A. Prophase

During which phase of mitosis do kinetochores appear at the centromere? A. Prophase B. Metaphase C. Anaphase D. Telophase

A. Prophase During prophase, kinetochores appear at the centromere. Kinetochores are protein structures located on the centromeres that serve as attachment points for specific fibers of the spindle apparatus appropriately called kinetochore fibers.

What is the longest phase of mitosis? A. Prophase B. Metaphase C. Anaphase D. Telophase

A. Prophase Prophase is the longest phase of mitosis, but it is faster than interphase.

During which phase of mitosis do the centriole pairs separate and move toward opposite poles? A. Prophase B. Metaphase C. Anaphase D. Telophase

A. Prophase The centriole pairs are paired cylindrical organelles that are located outside the nucleus in a region called the centrosome and are responsible for the correct division of DNA. Once the centrioles migrate to opposite poles of the cell, they begin to form spindle fibers. Each of the fibers radiate outward from the centrioles.

At which phase of meiosis does crossing over occur? A. Prophase I B. Metaphase I C. Anaphase I D. Telophase I

A. Prophase I During prophase I, homologous chromosomes can intertwine to form a tetrad; the homologous chromosomes are held together by a group of proteins called the synaptonemal complex. Chromatids of homologous chromosomes may break at the point of contact, called the chiasma and exchange equivalent pieces of DNA. This process is called crossing over, and can be characterized by the number of crossover events that occur in one strand of DNA, including single crossovers and double crossovers. Note that crossing over occurs between homologous chromosomes and NOT between sister chromatids of the same chromosome --- the latter are identical, so crossing over would not produce any change. Because of crossing over, each daughter cell will have a unique pool of alleles (genes coding for alternative forms of a given trait) from a random mixture of maternal and paternal origin. In classical genetics, crossing over explains Mendel's second law (of independent assortment), which states that the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes.

At which phase of meiosis do homologous chromosomes come together and intertwine in a process called synapsis? A. Prophase I B. Prophase II C. Metaphase I D. Metaphase II

A. Prophase I During prophase I, the chromatin condenses into chromosomes, the spindle apparatus forms, and the nucleoli and nuclear membrane disappear. The first major difference between meiosis and mitosis occurs at this point: homologous chromosomes come together and intertwine in a process called synapsis. At this point, each chromosome consists of two sister chromatids, so each synaptic pair contains four chromatids and is referred to as a tetrad.

During which phase of mitosis are sister chromatids pulled toward the opposite poles of the cell by shortening of the kinetochore fibers? A. Metaphase B. Anaphase C. Telophase D. Cytokinesis

B. Anaphase

Where are restriction points or checkpoints located in the cell cycle? I. G1/S II. G2/M III. S/M IV. G1/G2 A. I only B. I and II C. I, II, and III D. III and IV

B. I and II During the G1 stage, cells create organelles for energy and protein production (mitochondria, ribosomes, and endoplasmic reticulum), while also increasing their size. Passage into the S (synthesis) stage is governed by a restriction point, which determines if the DNA is in good enough condition for synthesis. If there is damage to the DNA, the cell cycle goes into arrest until the DNA has been repaired. The protein p53 is in control of this. During the G2 stage, the cell passes through another quality control checkpoint. DNA has already been duplicated during the S stage, and the cell checks to ensure that there are enough organelles and cytoplasm to divide between two daughter cells. The cell also checks to make sure DNA replication proceeded correctly to avoid passing on an error to daughter cells that may further replicate the error in their progeny. p53 also plays a role in the G2/M checkpoint.

In which phase of mitosis do the kinetochore fibers interact with the fibers of the spindle apparatus to align the chromosomes equidistant between the two poles of the cell? A. Prophase B. Metaphase C. Anaphase D. Telophase

B. Metaphase In metaphase, the centriole pairs are now at opposite ends of the cell. The kinetochore fibers interact with the fibers of the spindle apparatus to align the chromosomes at the metaphase plate (equatorial plate), which is equidistant between the two poles of the cell.

During which meiosis phase do homologous pairs (tetrads) align at the metaphase plate, and each pair attaches to a separate spindle fiber by its kinetochore? A. Prophase I B. Metaphase I C. Anaphase I D. Telophase I

B. Metaphase I During metaphase I, homologous pairs (tetrads) align at the metaphase plate, and each pair attaches to a separate spindle fiber by its kinetochore. Note the difference from mitosis: in mitosis, each chromosome is lined up on the metaphase plate by two spindle fibers (one from each pole); in meiosis, homologous chromosomes are lined up across from each other at the metaphase plate and are held by one spindle fiber.

What are spindle fibers made of? A. Microfilaments B. Microtubules C. Intermediate Filaments D. None of the above

B. Microtubules

What are centrioles made of? A. Microfilaments B. Microtubules C. Intermediate Filaments D. None of the above

B. Microtubules Centrioles are found in a region of the cell called the centrosome. They are the organizing centers for microtubules and are structured as nine triplets of microtubules with a hollow center. The centrosome is one of the two microtubule organizing centers of the cell --- the other being the basal body of the flagellum or cilium which are structured with nine pairs of microtubules forming an outer ring, with two microtubules in the center (known as the 9 + 2 structure). During mitosis, the centrioles migrate to opposite poles of the dividing cell and organize the mitotic spindle. The microtubules emanating from the centrioles attach to the chromosomes via complexes called kinetochores and can exert force on the sister chromatids, pulling them apart.

What is the shortest phase of mitosis? A. Prophase B. Metaphase C. Anaphase D. Telophase

C. Anaphase Anaphase is the shortest phase of mitosis. In anaphase, the sister chromatids are pulled apart to opposite ends of the cell.

In which phase of mitosis do the centromeres split so that each chromatid has its own distinct centromere? A. Prophase B. Metaphase C. Anaphase D. Telophase

C. Anaphase During anaphase, the centromeres split so that each chromatid has its own distinct centromere, thus allowing the sister chromatids to separate.

At which phase of meiosis do the homologous pair separate and are pulled to opposite poles of the cell in a process called disjunction? A. Prophase I B. Metaphase I C. Anaphase I D. Telophase I

C. Anaphase I During anaphase I, homologous pairs separate and are pulled to opposite poles. This process is called disjunction, and it accounts for Mendel's first law (of segregation). During disjunction, each chromosome of paternal origin separates (or disjoins) from its homologue of maternal origin, and either chromosome can end up in either daughter cell. Thus, the distribution of homologous chromosomes to the intermediate daughter cells is random with respect to parental origin. The separating of the two homologous chromosomes is referred to as segregation.

At which phase in meiosis can nondisjunction occur? A. Prophase I B. Metaphase I C. Anaphase I D. Telophase I

C. Anaphase I If, during anaphase I or II of meiosis, homologous chromosomes (anaphase I) or sister chromatids (anaphase II) fail to separate, one of the resulting gametes will have two copies of a particular chromosome and the other gamete will have none. Subsequently, during fertilization, the resulting zygote may have too many or too few copies of that chromosome. Nondisjunction can affect both autosomal chromosomes (such as trisomy 21, resulting in Down syndrome) and sex chromosomes (such as Klinefelter and Turner syndrome).

During which phase of meiosis do the cells become haploid and divide into two daughter cells by cytokinesis? A. Anaphase I B. Anaphase II C. Telophase I D. Telophase II

C. Telophase I During telophase I, a nuclear membrane forms around each new nucleus. At this point, each chromosome still consists of two sister chromatids joined at the centromere. The cells are now haploid; once homologous chromosomes separate, only n chromosomes are found in each daughter cell (23 in humans). The cell divides into two daughter cells by cytokinesis. Between cell divisions, there may be a short rest period, or interkinesis, during which the chromosomes partially uncoil. During telophase II, a nuclear membrane forms around each new nucleus. Cytokinesis follows, and two daughter cells are formed. Thus by completion of meiosis II, up to four haploid daughter cells are produced per gametocyte.

During which phase of mitosis does the separation of the cytoplasm and organelles occur so that each daughter cell has sufficient supplies to survive on its own? A. Metaphase B. Anaphase C. Telophase D. Cytokinesis

D. Cytokinesis At the end of telophase, cytokinesis is the separation of the cytoplasm and organelles so that each daughter cell has sufficient supplies to survive on its own. Each cell undergoes a finite number of divisions before programmed death. After that, the cell can no longer divide continuously.

What is the shortest phase of the cell cycle? A. G1 B. S C. G2 D. M

D. M M stage (Mitosis) is the shortest phase of the cell cycle.

During which phase of mitosis does the nuclear membrane reform around each set of chromosomes, and the nucleoli reappear? A. Prophase B. Metaphase C. Anaphase D. Telophase

D. Telophase

In which phase of mitosis does the spindle apparatus disappear? A. Prophase B. Metaphase C. Anaphase D. Telophase

D. Telophase

True or False: Cells that do not actively divide spend all of their time in an offshoot of G2 called G0.

False. Cells that do not actively divide spend all of their time in an offshoot of G1 called G0. During the G0 stage, the cell is simply living and serving its function, without any preparation for division.

True or False: Chromatin is the more condensed form of chromosomes.

False. Chromatin is the less condensed form of chromosomes. Heterochromatin is the more condensed form. During Interphase, chromosomes are in a less condensed form called chromatin, which allows for DNA to be available to RNA polymerase so that genes can be transcribed. Chromatin is not visible with light microscopy. During Mitosis, it is preferable to condense the DNA into tightly coiled chromosomes (heterochromatin) to avoid losing any genetic material during cell division.

True or False: There is no change in ploidy during meiosis.

False. During meiosis I the chromosome number is halved (reductional division) and the daughter cells have the haploid number of chromosomes (23 in humans). However, meiosis II is similar to mitosis in that sister chromatids are separated from one another; therefore, no change in plodiy is observed. It is critical to understand how meiosis I is different from mitosis! meiosis I goes from 2n ---> n meiosis II goes from n ---> n mitosis goes from 2n ---> 2n

True or False: During prophase the chromosomes uncoil and the spindle forms.

False. During prophase the chromosomes condense and the spindle forms. The first step in prophase involves condensation of the chromatin into chromosomes. Telophase is the reverse of prophase. The spindle apparatus disappears and the chromosomes uncoil.

True or False: Homologous chromosomes are identical copies of the same DNA that are held together at the centromere.

False. Homologous chromosomes are related chromosomes of opposite parental origin (such as maternal chromosome 15 and paternal chromosome 15, or - in males- the X and Y chromosomes) Sister chromatids are identical copies of the same DNA that are held together at the centromere. After S phase, a cell contains 92 chromatids, 46 chromosomes, and 23 homologous pairs.

True or False: Meiosis occurs in gametocytes (germ cells) and results in up to two nonidentical sex cells (gametes).

False. Meiosis occurs in gametocytes (germ cells) and results in up to four nonidentical sex cells (gametes). Where as mitosis occurs in somatic tissues and results in two identical daughter cells, meiosis occurs in gametocytes (germ cells) and results in up to four nonidentical sex cells (gametes). In contrast to mitosis, which consists of one round each of replication and division, meiosis consists of one round of replication followed by two rounds of division.

True or False: Mitosis occurs in germ cells, or cells that are involved in sexual reproduction.

False: Mitosis occurs in somatic cells, or cells that are not involved in sexual reproduction. Mitosis is the process by which two identical daughter cells are created from a single cell.

Is Meiosis I or Meiosis II similar to mitosis?

Meiosis II is similar to mitosis, in that it results in the separation of sister chromatids, and is known as equational division. Meiosis I results in homologous chromosomes being separated, generating haploid daughter cells; this is known as reductional division.

True or False: After S phase there are 92 chromatids organized into 46 chromosomes, which are organized into 23 homologous pairs.

True. After S phase there are 92 chromatids organized into 46 chromosomes, which are organized into 23 homologous pairs.

True or False: Meiosis II is very similar to mitosis in that sister chromatids --- rather than homologues --- are separated from each other.

True. Meiosis II is very similar to mitosis in that sister chromatids --- rather than homologues --- are separated from each other. Prophase II: The nuclear envelope dissolves, nucleoli disappear, the centrioles migrate to opposite poles, and the spindle apparatus begins to form. Metaphase II: The chromosomes line up on the metaphase plate. Anaphase II: The centromeres divide, separating the chromosomes into sister chromatids. These chromatids are pulled to opposite poles by spindle fibers Telophase II: A nuclear membrane forms around each new nucleus. Cytokinesis follows, and two daughter cells are formed. Thus by completion of meiosis II, up to four haploid daughter cells are produced per gametocyte.

True or False: The completion of mitosis results in two identical daughter cells.

True. The completion of mitosis results in two identical daughter cells. Mitosis occurs in somatic tissues and results in two identical daughter cells, meiosis occurs in gametocytes (germ cells) and results in up to four nonidentical sex cells (gametes).

True or False: The further apart two genes are, the more likely they are to become unlinked during crossing over.

True. The further apart two genes are, the more likely they are to become unlinked during crossing over. The rate of gene unlinking is used to map differences between two genes. The further apart two genes are, the more likely they are to become unlinked during crossing over. These statistics can then be used to determine the distance between genes on the chromosome, measured in units called centimorgans. Such genetic recombination (like crossing over) can unlink genes, thereby increasing the variety of genetic combinations that can be produced via gametogensis. Linkage refers to the tendency for genes to be inherited together; genes that are located further from each other physically are less likely to be inherited together, and are more likely to undergo crossing over relative to each other.

True or False: After meiosis I there are two haploid daughter cells, and after meiosis II there are up to four haploid gametes.

True: After meiosis I there are two haploid daughter cells, and after meiosis II there are up to four haploid gametes.

True or False: During the S (synthesis) stage, the cell replicates its genetic material resulting in each chromosome consisting of two identical chromatids (sister chromatids) that are bound together at a specialized region known as the centromere.

True: During the S (synthesis) stage, the cell replicates its genetic material resulting in each chromosome consisting of two identical chromatids (sister chromatids) that are bound together at a specialized region known as the centromere.