chapter 3 (test 1)

With regard to sister chromatids, which phase of mitosis is the organization phase, and which is the separation phase?

Metaphase is the organization phase and anaphase is the separation phase

What is a sister chromatid? Are sister chromatids genetically similar or identical? Explain.

Sister chromatids are identical copies derived from the replication of a parental chromosome. They remain attached to each other at the centromere. They are genetically identical, barring rare mutations and crossing over with homologous chromosomes.

A cell has four pairs of chromosomes. Assuming that crossing over does not occur, what is the probability that a gamete will contain all of the paternal chromosomes? If n equals the number of chromosomes in a set, which of the following expressions can be used to calculate the probability that a gamete will receive all of the

(1/2)n = (1/2)4 = 1/16 or 6.25% C18 During prophase II, your drawing should show four replicated chromosomes (i.e., four structures that look like Xs). Each chromosome is one homolog. During prophase of mitosis, there should be eight replicated chromosomes (i.e., eight Xs). During prophase of mitosis, there are pairs of homologs. The main difference is that prophase II has a single copy of each of the four chromosomes, whereas prophase of mitosis has four pairs of homologs. At the end of meiosis I, each daughter cell has received only one copy of a homologous pair, not both. This is due to the alignment of homologs during metaphase I and their separation during anaphase I.

How does the attachment of kinetochore microtubules to the kinetochore differ in metaphase of meiosis I from metaphase of mitosis? Discuss what you think would happen if a sister chromatid was not attached to a kinetochore microtubule.

: In metaphase I of meiosis, each pair of chromatids is attached to only one pole via the kinetochore microtubules. In metaphase of mitosis, there are two attachments (i.e., to both poles). If the attachment was lost, a chromosome would not migrate to a pole and may not become enclosed in a nuclear membrane after telophase. If left out in the cytosol, it would eventually be degraded

How many sets of chromosomes are found in a human somatic cell, and how many chromosomes are within one set? A. 2 sets, with 23 in each set B. 23 sets, with 2 in each set C. 1 set, with 23 in each set D. 23 sets, with 1 in each set

A

. Three genes (A, B, and C) are found on three different chromo somes. For the following diploid genotypes, describe all of the posSible gamete combinations. A. Bb cc B. AA Bb CC C. Aa BB cc D. Aa bb cc

A. A B C, A B c, A b C, A b c, a B C, a b C, a B c, a b c B. A B C, A b C C. A B C, A B c, a B C, a B c D. A b c, a b c

For the following events, specify whether they occur during mitosis; meiosis I, or meiosis Il: A. Separation of conjoined chromatids within a pair of sister chromatids B. Pairing of homologous chromosomes C. Alignment of chromatids along the metaphase plate D. Attachment of sister chromatids to both poles

A. During mitosis and meiosis II B. During meiosis I C. During mitosis, meiosis I, and meiosis II D. During mitosis and meiosis II

What would be the sex of a human with the following numbers of sex chromosomes? A. XXX B. X (also described as XO) C. XYY D. XXY

A. Female; there are no Y chromosomes. B. Female; there are no Y chromosomes. C. Male; the Y chromosome determines maleness. D. Male; the Y chromosome determines maleness

A pea plant has the genotype TtRr. The independent assortment of these two genes occurs at because chromosomes carrying the alleles line up independently of the chromosomes carrying the alleles. A. metaphase of meiosis I, T and t, R and r B. metaphase of meiosis I, T and R, t and r C. metaphase of meiosis II, T and t, R and r D. metaphase of meiosis II, T and R, t and r

A. metaphase of meiosis I, T and t, R and r

In mammals, sex is determined by A.the Sry gene on the Y chromosome. B. having two copies of the X chromosome. C. having one copy of the X chromosome. D. both a and c.

A.the Sry gene on the Y chromosome.

Binary fission is a form of asexual reproduction. is a way for bacteria to reproduce. begins with a single mother cell and produces two genetically identical daughter cells. is all of the above.

AOA

Let's suppose that a gene affecting pigmentation is found on the X chromosome (in mammals or insects) or the Z chromosome (in birds) but not on the Y or W chromosome. It is found on an autosome in bees. This gene exists in two alleles; D (dark), is dominant to d (light). What would be the phenotypic results of crosses between a true-breeding dark female and true-breeding light male, and the reciprocal crosses involving a true-breeding light female and true-breeding dark male, in the following species?

All dark offspring; reciprocal: dark females and light males

Which phase of mitosis??

Anaphase

What critical event occurs during the S phase of the eukaryotic cell cycle? A. Cells make a decision of whether or not to divide. B. DNA replication produces pairs of sister chromatids. C. The chromosomes condense. D. The single nucleus is divided into two nuclei.

B. DNA replication produces pairs of sister chromatids.

An abnormal fruit fly has two sets of autosomes and is XXY. Such a fly would be A. a male. B. a female. C. a hermaphrodite. D. none of the above.

B. Female

Which of the following is the correct order of phases of the cell cycle? G1, G2, S, M G1, S, G2, M G1, G2, M, S G1, S, M, G2

B. G1, S , G2, M

Eukaryotic cells must sort their chromosomes during mitosis so each daughter cell receives the correct number of chromosomes. Why don't bacteria need to sort their chromosomes?

Bacteria do not need to sort their chromosomes because they only have one type of chromosome.

Which of the following is not found in a prokaryotic cell? A. Plasma membrane B. Ribosome C. Cell nucleus C. Cytoplasm

C. Cell nucleus

Which of the following is not one of the tenets of the chromosome theory of inheritance? A. Chromosomes contain the genetic material that is transmitted from parent to offspring and from cell to cell. B. Chromosomes are replicated and passed along, generation after generation, from parent to offspring. C. Chromosome replication occurs during the S phase of the cell cycle. D. Each parent contributes one set of chromosomes to its offspring.

C. Chromosome replication occurs during the S phase of the cell cycle.

In animals, a key difference between spermatogenesis and oogenesis is that A. only oogenesis involves meiosis. B. only spermatogenesis involves meiosis. C. spermatogenesis produces four sperm, whereas oogenesis produces only one egg cell. D. None of the above.

C. spermatogenesis produces four sperm, whereas oogenesis produces only one egg cell.

What is the function of microtubules during mitosis? A. Aster microtubules are important for the positioning of the spindle apparatus within an animal cell and in the process of cell division. B. Polar microtubules play a role in the separation of the two poles. C. Kinetochore microtubules aid in the alignment of chromosomes during metaphase and the movement of individual chromosomes toward a pole during anaphase. D. All of the above

D. AOA

When preparing a karyotype, which of the following steps is conducted? A. Treat the cells with drugs that cause them to begin cell division. B. Treat the cells with a hypotonic solution that causes them to swell. C. Expose the cells to chemical dyes that bind to the chromosomes and stain them. D. All of the above.

D. All of the Above

Which of the following statements regarding plants is false? A.Meiosis within anthers produces spores that develop into pollen. B.Meiosis within ovules produces spores that develop into an embryo sac. c. The male gametophyte is a pollen grain, and the female gametophyte is an embyro sac. D. Meiosis directly produces sperm and egg cells in plants.

D. Meiosis directly produces sperm and egg cells in plants.

Why is it necessary for the chromosomes to condense during mitosis and meiosis? What do you think might happen if the chromosomes were not condensed?

During interphase, the chromosomes are greatly extended. In this conformation, they might get tangled up with each other and not sort properly during meiosis and mitosis. The condensation process probably occurs so that the chromosomes easily align along the equatorial plate during metaphase without getting tangled up.

Describe the timing of meiosis I and Il during human oogenesis.

During oogenesis in humans, the cells are arrested in prophase I of meiosis for many years until selected primary oocytes progress through the rest of meiosis I and begin meiosis II. If fertilization occurs, meiosis II is completed.

A diploid species has four chromosomes per set for a total of eight chromosomes in its somatic cells. Draw the cell as it would look in late prophase of meiosis II and prophase of mitosis. Discuss how prophase of meiosis II and prophase of mitosis differ from each other, and explain how the difference originates.

During prophase II, your drawing should show four replicated chromosomes (i.e. four structures that look like Xs). Each chromosome is one homog. During prophase of mitosis, there should be eight replicated chromosomes. During prophase of mitosis, there are pairs of homologs. The main difference is that prophase II has a single copy of each of the four choromosomes, whereas prophase of mitosis has four pairs of homologs. At the end of meiosis I, each daughter cell has received only one copy of homogous pair, not both. This is due to the alignment of homlogs during metaphase I and their separation during anaphase I.

A species is diploid and has three chromosomes per set. Draw what the chromosomes would look like in the G and G phases of the cell cycle

In G1, there should be six linear chromosomes. In G2, there should be 12 chromatids that are attached to each other in pairs of sister chromatids.

The arrangement of homologs during metaphase of meiosis I is a random process. In your own words, explain what this means.

It means that the maternally derived and paternally derived chromosomes are randomly aligned along the metaphase plate during metaphase I

A eukaryotic cell is diploid containing 10 chromosomes (5 in each set). For mitosis and meiosis, how many daughter cells would be produced, and how many chromosomes would each one contain?

Mitosis—two diploid cells containing 10 chromosomes each (two complete sets). Meiosis—four haploid cells containing 5 chromosomes each (one complete set)

The period between meiosis I and meiosis II is called interphase II. Does DNA replication take place during interphase II?

No

The arctic fox has 50 chromosomes (25 per set), and the common red fox has 38 chromosomes (19 per set). These species can interbreed to produce viable but infertile offspring. How many chromosomes would the offspring have? What problems do you think may occur during meiosis that would explain the offspring's infertility?

The hybrid offspring would have 44 chromsomes (i.e. 25+19). The reason for infertility is because each chromosome does not have a homologous partner. Therefore, the chromosomes cannot properly pair during metaphase I, and the gametes do not receive one copy of each homolog. Gametes will be missing certain chromosomes, which makes them infertile.

Explain why the products of meiosis may not be genetically identical, whereas the products of mitosis are.

The products of meiosis have only one copy of each type of chromosome. For example, one human gamete may contain the paternally derived copy of chromosome 11, whereas a different gamete may contain the maternally derived copy of chromosome 11. These two homologs may carry different alleles of the same genes and therefore are not identical. In contrast, mitosis produces genetically identical daughter cells that have both copies of all the pairs of homologous chromosomes.

Describe the key events during meiosis that result in a 50% reduction in the amount of genetic material per cell.

The reduction occurs because there is a single DNA replication event but 2 cell divisions. Because of the nature of separation during anaphase I, each cell receives one copy of each chromosome

What is a homolog? With regard to genes and alleles, how are homologs similar to and different from each other?

The term homolog refers to the members of a chromosome pair. Homologs are usually the same size and carry the same types and order of genes. They may differ in that the genes they carry may be different alleles.

If a diploid cell contains six chromosomes (i.e., three per set), how many possible random arrangements of homologs could occur during metaphase of meiosis I?

There are three pairs of chromosomes. The number of different, random alignments equals 2n, where n equals the number of chromosomes per set. So the possible number of arrangements equals 23, which is 8.

. A phenotypically normal woman with an abnormally long chromosome 13 (and a normal homolog of chromosome 13) marries a phenotypically normal man with an abnormally short chromosome 11 (and a normal homolog of chromosome I l). What is the probability of producing an offspring that will have both a long chromosome 13 and a short chromosome Il? If such a child is produced, what is the probability that this child would eventually pass both abnormal chromosomes to one of his or her offspring?

There is a 1/2 chance that the mother will transmit her abnormal chromosome and a 1/2 chance that the father will. We use the product rule to calculate the chances of both events happening. So the answer is 1/2 × 1/2 = 1/4, or 25%. The probability that such a child will pass both chromosomes to an offspring is also 25% because that child had a 1/2 chance of passing either chromosome.

Nine-banded armadillos almost always give birth to four offspring that are genetically identical quadruplets. Explain how you think this happens

To produce identical quadruplets, fertilization begins with one sperm and one egg cell. This fertilized egg then could divide twice by mitosis to produce four genetically identical cells. These four cells could then separate from each other to begin the lives of four distinct individuals. Another possibility is that mitosis could produce two cells that separate from each other. These two cells could then divide by mitosis to produce two pairs of cells, which could also separate to produce four individual cells.

At puberty, the testes contain a finite number of cells and produce an enormous number of sperm cells during the life span of a male. Explain why testes do not run out of spermatogonial cells.

to produce sperm, a spermatogonial cell first goes through mitosis to produce two cells. one of these remains a spermatogonial cell and the other progresses through meiosis. in this way, the testes continue to maintain a population of spermatogonial cells.