Chapter 2: Mitosis and Meiosis

The __________ is a cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division.

mitotic spindle(s)

If a typical somatic cell has 64 chromosomes, how many chromosomes are expected in each gamete of that organism?

32

G2 Phase

- Cell prepares for mitosis. - The volume of the cell has roughly doubled

Anaphase

- Cohesins break down. - Kinetochores move toward poles of cell.

Prophase

- Cohesins join sister chromatids of duplicated chromosome. - Tubulins assemble into spindle microtubules.

M Phase

- The centrosomes move away from each other toward the poles of the cell, in the process organizing the formation of the mitotic spindle. - When mitosis is complete, the cell divides (cytokinesis), forming two genetically identical daughter cells.

You are given a metaphase chromosome preparation (a slide) from an unknown organism that contains 12 chromosomes. Two that are clearly smaller than the rest appear identical in length and centromere placement. What would most likely be true of these two chromosomes?

- They would replicate synchronously during the S phase of the cell cycle. - They are homologous chromosomes. - They have similar banding patterns.

Homologous Chromosomes

- in a pair, one is of maternal origin, the other of paternal origin - crossover between them contributes to genetic diversity - separate during anaphase I of meiosis

Sister Chromatids

- separate during anaphase II of meiosis - contain identical nucleotide sequences prior to crossing over - separate during anaphase of mitosis

Which list of steps in the eukaryotic cell cycle is given in the correct order? (step order listed left to right)

. . . G1 - S - G2 - M - G1 . . . (The S phase is both preceded and followed by a period of growth (G1 and G2, respectively). After the M phase, the cell re-enters the G1 phase.)

If one follows 180 primary oocytes in an animal through their various stages of oogenesis, how many secondary oocytes would be formed? How many first polar bodies would be formed? How many ootids would be formed?

180 180 180

The diploid chromosome number of an organism is usually represented as 2n. Humans have a diploid chromosome number of 46. What would be the expected haploid chromosome number in a human?

23

If one follows 180 primary spermatocytes in an animal through their various stages of spermatogenesis, how many secondary spermatocytes would be formed? How many spermatids would be formed?

360 720

During oogenesis in an animal species with a haploid number of 6, one dyad undergoes nondisjunction during meiosis II. Following the second meiotic division, this dyad ends up intact in the ovum. How many chromosomes are present in the second polar body?

5

During oogenesis in an animal species with a haploid number of 6, one dyad undergoes nondisjunction during meiosis II. Following the second meiotic division, this dyad ends up intact in the ovum. How many chromosomes are present in the mature ovum?

7

Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair includes a maternal and a paternal member (e.g., Am and Ap.) How many possible combinations of the three sets of dyads will result after the completion of anaphase I?

8

Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair includes a maternal and a paternal member (e.g., Am and Ap.) During meiosis I, assuming no crossing over, what chromatid combination(s) will be present at the completion of prophase I?

Am Ap Bm Bp Cm Cp

G1 Checkpoint

Cell commits to go through the cycle.

During interphase of the cell cycle, ________.

DNA content essentially doubles.

S Phase

DNA replicates.

True of False: The longest stage of interphase is G2.

False (The longest stage of interphase is S; cells typically spend about 7 hours in this stage. The shortest stage of interphase is G2 (3 hours), although the shortest stage of the entire cell cycle is mitosis (1 hour).)

True of False: Haploid cells do not undergo mitosis.

False (Both haploid and diploid cells can undergo mitosis.)

When cells withdraw from the continuous cell cycle and enter a "quiescent" phase, they are said to be in what stage?

G0

During which stage can cells either exit the cell cycle or become committed to completing the cell cycle?

G1 (Cells can exit the cell cycle and enter G0 or be committed to initiate DNA synthesis late in G1.)

From which phase of the cell cycle does a cell enter G0 phase?

G1 Phase

Metaphase

Kinetochores are motionless in relation to poles of cell.

Pro-metaphase

Microtubules attach to kinetochores.

G1 Phase

Non-dividing cells exit cell cycle.

Which condition is evaluated at the G2/M checkpoint?

Precise replication of DNA.

What is true about the second meiotic division?

Sister chromatids are pulling apart.

Telophase

Spindle microtubules disassemble.

True or False: A chromosome may contain one or two chromatids in different phases of the mitotic or meiotic cell cycle.

True

True or False: The end result of meiosis is four haploid daughter cells.

True

True or False: Crossing over occurs during early prophase I when homologous chromosomes loosely pair up along their lengths. Crossing over occurs only between nonsister chromatids within a homologous pair of chromosomes, not between the sister chromatids of a replicated chromosome. Crossing over is reduced near the centromere; segments that are not adjacent to the centromere (for example, segments near the ends of chromosomes) are more likely to cross over.

True

True or False: DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II.

True (During anaphase of both meiosis I and meiosis II, the DNA content (number of copies of chromosomes) in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set).)

Separation of sister chromatids occurs _________.

at anaphase in mitosis and anaphase II in meiosis

The centromere of a chromosome separates during __________.

anaphase

After chromosomes condense, the __________ is the region where the identical DNA molecules are most tightly attached to each other.

centromere(s)

The __________ are the organizing centers for microtubules involved in separating chromosomes during mitosis.

centrosome(s)

What are the areas where chromatids intertwine during meiosis called?

chiasma

Name two cellular organelles, each containing genetic material, which are involved in either photosynthesis or respiration.

chloroplasts and mitochondria

During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called __________.

chromatin

In most eukaryotes, division of the nucleus is followed by __________ , when the rest of the cell divides.

cytokinesis

Living organisms are categorized into two major groups based on the presence or absence of a nucleus. What group is defined by the presence of a nucleus?

eukaryotic organism

In dividing cells, most of the cell's growth occurs during __________.

interphase

During mitosis, microtubules attach to chromosomes at the ___________.

kinetochore(s)

Each of the following events occurs during mitosis except _______. nuclear membrane breaks down microtubules assemble between centrioles chromosomes condense polar microtubules contract, pulling attached chromosomes toward the poles

polar microtubules contract, pulling attached chromosomes toward the poles (This describes the role of kinetochore microtubules during anaphase. Polar microtubules lengthen during anaphase, causing the cell to become elliptical.)

Novel combinations of genes can arise from _________.

reciprocal exchange of DNA between homologs during prophase I

Which of the following cell structures is directly involved in protein synthesis?

rough endoplasmic reticulum and ribosomes (Ribosomes are the sites of protein translation, and some ribosomes attach to the rough endoplasmic reticulum.)

DNA replication produces two identical DNA molecules, called, ____________ which separate during mitosis.

sister chromatid(s)

During oogenesis in an animal species with a haploid number of 6, one dyad undergoes nondisjunction during meiosis II. Following the second meiotic division, this dyad ends up intact in the ovum. Following fertilization by a normal sperm, what chromosome condition is temporarily created?

trisomy