Question 1

During which of the following stages of the cell cycle would a chromosome consist of only a single chromatid?

Accepted Answer

During the G1 phase of the cell cycle, each chromosome consists of a single chromatid. After DNA replication in the S phase, chromosomes consist of two sister chromatids.

Question 2

The cells that undergo meiosis in males are

Accepted Answer

Spermatocytes are the cells in males that undergo meiosis to produce spermatids, which eventually develop into mature sperm. Spermatogonia are the precursor cells that divide mitotically to produce spermatocytes. Spermatids are the result of meiosis and undergo further development but do not undergo meiosis themselves. Oocytes are female germ cells that undergo meiosis to produce ova, not related to male gametogenesis. Sperm are the final, mature male gametes and do not undergo meiosis.

Question 3

Microtubules that originate at opposite centrosomes and interdigitate near the cell's equator without attaching to chromosomes are the

Accepted Answer

Polar microtubules are the ones that originate from opposite centrosomes and interdigitate at the cell's equator, playing a role in separating the two poles by pushing against each other without attaching to chromosomes.

Question 4

Crossing-over between homologous chromosomes occurs at which of the following stages of meiosis?

Accepted Answer

Crossing-over, the exchange of genetic material between homologous chromosomes, occurs during prophase I of meiosis, facilitating genetic diversity in the resulting gametes.

Question 5

Nondisjunction can occur at either the first or second division of meiosis.XXY individuals could arise from nondisjunction at the ________ meiotic division in the ________.

Accepted Answer

Nondisjunction at either the first or second meiotic division in either the mother or the father can lead to the formation of XXY individuals. In the mother, nondisjunction at the first division would result in an egg with two X chromosomes, and in the father, nondisjunction at the first division would result in a sperm with both an X and a Y chromosome. Similarly, nondisjunction at the second division in either parent could also lead to gametes with an extra X chromosome, which, when fertilized, would result in an XXY individual.

Question 6

The stage of mitosis when sister chromatids separate from each other and migrate to opposite poles of a cell is called

Accepted Answer

During anaphase, sister chromatids separate and move to opposite poles of the cell, which is a key step in cell division during mitosis.

Question 7

A chromosome with two arms of similar length is referred to as

Accepted Answer

A chromosome with two arms of similar length is referred to as metacentric. This means the centromere is approximately in the middle, making the two arms of the chromosome appear almost equal in length.

Question 8

The chromosomal structure to which spindle fibers attach during the mitotic divisions is the

Accepted Answer

The kinetochore is the specific structure on chromosomes where spindle fibers attach during mitosis to pull the chromosomes apart.

Question 9

In Drosophila virilis, somatic cell nuclei contain 12 chromosomes while sperm nuclei contain only 6 chromosomes.What does n equal for this species?

Accepted Answer

n equals the number of chromosomes in a haploid cell, which for Drosophila virilis is 6, as seen in the sperm nuclei.

Question 10

Mitosis results in ________ chromosome number, whereas meiosis results in ________ chromosome number.

Accepted Answer

Mitosis results in two daughter cells each having the same number of chromosomes as the parent cell, thus there is no change in chromosome number. Meiosis, on the other hand, results in four daughter cells each with half the number of chromosomes of the parent cell, thus reducing the chromosome number by half.

Question 11

Which types of chromosomes provide the basis for sex determination in most mammals?

Accepted Answer

In most mammals, sex determination is based on the presence of sex chromosomes, with the typical configuration being XX for females and XY for males.

Question 12

Premeiotic germ cells that divide mitotically in females are

Accepted Answer

Oogonia are the premeiotic germ cells in females that divide mitotically to produce primary oocytes.

Question 13

The mitotic stage during which chromosomes begin attaching to spindle fibers and moving randomly and reversibly to the centrosomes is

Accepted Answer

During prometaphase, the nuclear envelope breaks down, allowing the chromosomes to attach to spindle fibers. This attachment facilitates their movement towards the centrosomes, a process that is indeed random and reversible until they align at the metaphase plate.

Question 14

Which of the following events occurs during mitosis but not during meiosis?

Accepted Answer

During mitosis, sister chromatids segregate, and chromosomes align on the metaphase plate, which also occurs in meiosis. Homologous chromosomes pairing and crossing-over are specific to meiosis, not mitosis. Therefore, none of the choices listed occurs exclusively during mitosis.

Question 15

Humans have 22 pairs of autosomes plus one sex chromosome pair.How many autosomes are present in a normal human primary spermatocyte?

Accepted Answer

The answer of Humans have 22 pairs of autosomes plus...

Question 16

Nondisjunction can occur at either the first or second division of meiosis.XYY individuals would most likely arise from nondisjunction at the ________ meiotic division in the ________.

Accepted Answer

Nondisjunction at the second meiotic division in the father can lead to the production of sperm with an extra Y chromosome, resulting in an XYY individual when one of these sperm fertilizes a normal egg.

Question 17

The stage of mitosis when chromosomes condense to form rod-shaped structures visible under the microscope is called

Accepted Answer

During prophase, the first stage of mitosis, chromosomes condense and become visible under a light microscope as rod-shaped structures. This is a key preparatory step for the chromosomes to be properly aligned and separated into the daughter cells.

Question 18

Drosophila melanogaster has four pairs of chromosomes (including a pair of sex chromosomes).Sperm from this species are formed by a meiotic process in which homologous chromosomes pair and segregate but do not undergo crossing-over.How many genetically different kinds of sperm could be produced by a Drosophila melanogaster male (XY)?

Accepted Answer

In Drosophila melanogaster, there are 4 pairs of chromosomes. During meiosis, each pair can segregate independently, leading to 2^4 = 16 different combinations of chromosomes in the sperm.

Question 19

At which of the following stages of meiosis would homologous chromosomes be paired?

Accepted Answer

Homologous chromosomes pair up during prophase of meiosis I and align together at the metaphase plate during metaphase of meiosis I. This pairing is crucial for the process of crossing over and genetic recombination.

Question 20

Which of the following statements applies to homologous nonsister chromatids?

Accepted Answer

Homologous nonsister chromatids contain the same genes in the same order but may have different alleles, as they come from homologous chromosomes, one from each parent.

Quiz 4: The Chromosome Theory of Inheritance