Chapter 2

Question 1

Which of the following statements is false?

a. Errors in chromosome separation are rarely a problem for an organism.
b. Errors in chromosome separation can result in a miscarriage.
c. Errors in chromosome separation can result in cancer.
d. Errors in chromosome separation can result in a child with severe handicaps.
Errors in chromosome separation can cause numerous problems for an organism.

Answer 1

a. Errors in chromosome separation are rarely a problem for an organism.

Question 2

Which of these are NOT prokaryotes?

a. Eubacteria
b. Archaea
c. Viruses
d. Ancient bacteria

Answer 2

c. Viruses

Question 3

Which statement is true?

a. Eubacteria are more closely related to archaea than they are to eukaryotes.
b. Archaea are more closely related to eukaryotes than they are to eubacteria.
c. Eukaryotes are more closely related to eubacteria than they are to archaea.
d. Viruses are more closely related to prokaryotes than they are to eukaryotes.
e. Eubacteria, archaea, and eukaryotes are all equally related.

Answer 3

b. Archaea are more closely related to eukaryotes than they are to eubacteria.

Question 4

Which of the following statements is false?

a. Generally, chromosomes of prokaryotes are circular.
b. Prokaryotes usually have a single molecule of DNA.
c. Generally, chromosomes of eukaryotes are circular.
d. Eukaryotes usually have multiple chromosomes.
e. Eukaryote chromosomes are usually linear.

Answer 4

c. Generally, chromosomes of eukaryotes are circular.

Question 5

In eukaryotes, chromosomes do not contain

a. ribosomes.
b. chromatin.
c. proteins.
d. histones.
e. DNA.

Answer 5

a. ribosomes.

Question 6

Prokaryotic chromosomes do not have telomeres because they

a. do not go through mitosis.
b. do not go through DNA replication.
c. are in the cytoplasm.
d. are circular.
e. have no centromeres.

Answer 6

d. are circular.

Question 7

In prokaryotes, replication usually begins at a specific place on the chromosome called the

a. binary fission site.
b. origin of replication.
c. origin of mitosis.
d. anchoring site.
e. kinetochore.

Answer 7

b. origin of replication.

Question 8

The highly organized internal scaffolding of the nucleus is called the

a. histone complex.
b. spindle microtubules.
c. nuclear cohesion.
d. nuclear matrix.
e. nuclear envelope.

Answer 8

d. nuclear matrix.

Question 9

The attachment point on the chromosome for spindle microtubules is the

a. telomere.
b. centromere.
c. origin of replication.
d. sister chromatid.
e. allele.

Answer 9

b. centromere.

Question 10

The process of splitting the cytoplasm, which separates one cell into two, is termed

a. cytokinesis.
b. mitosis.
c. anaphase.
d. diakinesis.
e. fusion.

Answer 10

a. cytokinesis.

Question 11

In order to be functional, a eukaryotic chromosome requires all of the following except

a. a centromere.
b. origins of replication.
c. a plasmid.
d. telomeres.

Answer 11

c. a plasmid.

Question 12

Diploid cells are cells with

a. a single set of chromosomes.
b. circular chromosomes.
c. two sets of chromosomes.
d. many sets of chromosomes.
e. three sets of chromosomes

Answer 12

c. two sets of chromosomes.

Question 13

If a healthy cell passes the G1/S checkpoint,

a. it will enter the G0 stage of the cell cycle.
b. DNA will be replicated.
c. it will not divide.
d. it will proceed immediately to cytokinesis.
e. it will die.

Answer 13

b. DNA will be replicated.

Question 14

Which of the following does NOT occur during the G2 phase of the cell cycle?

a. The G2/M checkpoint is reached.
b. DNA replication and error checking is completed.
c. The cell completes preparation for mitosis.
d. The cell divides.

Answer 14

d. The cell divides.

Question 15

Which of the following occurs during prometaphase?

a. The chromosomes align in a single plane.
b. DNA is replicated.
c. Microtubules attach to the kinetochores.
d. Mitotic spindles form.
e. The two sister chromatids separate.

Answer 15

c. Microtubules attach to the kinetochores.

Question 16

Chromosome movement during anaphase is a result of

a. disassembly of tubulin molecules by molecular motor proteins.
b. kinetochore shortening causing chromosomes to pull apart.
c. metaphasal plate splitting resulting in chromosomal disassembly.
d. the cohesion protein attaching to the centromeres of sister chromatids.
e. cilia movement inside the cellular structure.

Answer 16

a. disassembly of tubulin molecules by molecular motor proteins.

Question 17

Pea plants have seven different types of chromosomes. A chromosome with a centromere at the very end is called

a. submetacentric.
b. metacentric.
c. acrocentric.
d. acentric.
e. telocentric.

Answer 17

e. telocentric.

Question 18

A dividing eukaryotic cell is treated with a drug that inhibits the molecular motors associated with kinetochores. At which cell cycle stage would it stop?

a. G1
b. S
c. G2
d. M (metaphase)
e. M (telophase)

Answer 18

d. M (metaphase)

Question 19

Pea plants have seven different types of chromosomes. The nucleus of a megaspore in a pea ovary would contain how many chromosomes?

a. 3 ½
b. 7
c. 14
d. 21
e. 30

Answer 19

b. 7

Question 20

Pea plants have seven different types of chromosomes. A nucleus in the pea endosperm contains how many chromosomes?

a. 3 ½
b. 7
c. 14
d. 21
e. 30

Answer 20

d. 21

Question 21

What process is unique to plants?

a. Meiosis
b. Double fertilization
c. Crossing over
d. Haploid gametes
e. Spermatogenesis

Answer 21

b. Double fertilization

Question 22

Suppose that a diploid cell contains 8 chromosomes (2n = 8). How many different combinations in the gametes are possible?

a. 2
b. 4
c. 8
d. 16
e. 64

Answer 22

d. 16

Question 23

In a flowering plant, the male part of the flower (the stamen) produces haploid microspores that divide by _____to produce sperm.

a. mitosis
b. meiosis
c. gametogenesis
d. spermatogenesis
e. fertilization

Answer 23

a. mitosis

Question 24

A pollen grain that lands on a stigma grows a pollen tube to deliver ___ (how many?) sperm to the ovary. Fusion of a sperm with an egg produces a ___ n cell called a___.

a. 1; 1; zygote
b. 2; 1; megasporocyte
c. 2; 2; zygote
d. 1; 2; microsporocyte
e. 1; 2; megasporocyte

Answer 24

c. 2; 2; zygote

Question 25

To provide food for the developing embryo, a tissue called endosperm is produced through double fertilization. Endosperm has a ploidy of a. 1n. b. 2n. c. 3n. d. 4n. e. 5n.

Answer 25

c. 3n.

Question 26

What might be the result if breakdown of the shugoshin protein were premature? a. The cohesion protein would hold the chromosome arms together longer. b. The separation of homologous chromosomes would occur prematurely. c. The separation of sister chromatids would occur prematurely. d. Spindle fibers wouldn’t form. e. Sister chromatids would never separate.

Answer 26

c. The separation of sister chromatids would occur prematurely.

Question 27

A diploid somatic cell from a rat has a total of 42 chromosomes (2n = 42). As in humans, sex chromosomes determine sex: XX in females and XY in males. What is the total number of telomeres in a rat cell in G2? a. 21 b. 42 c. 84 d. 126 e. 168

Answer 27

e. 168

Question 28

A diploid somatic cell from a rat has a total of 42 chromosomes (2n = 42). As in humans, sex chromosomes determine sex: XX in females and XY in males. What is the total number of chromosomes present in the cell during metaphase I of meiosis? a. 21 b. 42 c. 84 d. 126 e. 168

Answer 28

b. 42

Question 29

A diploid somatic cell from a rat has a total of 42 chromosomes (2n = 42). As in humans, sex chromosomes determine sex: XX in females and XY in males. What is the total number of chromosomes in a polar body cell from a rat? a. 21 b. 40 c. 41 d. 42 e. 84

Answer 29

a. 21

Question 30

What evidence is there that viruses evolved after, not before, cells?

Answer 30

Viruses can reproduce only within host cells. Thus, they must have evolved after cells.

Question 31

Why is mitosis important within the cell cycle?

Answer 31

A single cell and all its genetic information is duplicated. Each cell contains a full complement of chromosomes.

Question 32

Explain why mitosis does not produce genetic variation and how meiosis leads to the production of tremendous genetic variation.

Answer 32

Mitosis produces cells that are genetically identical to the parent cell. Meiosis includes two distinct processes that contribute to the generation of genetic variation: Crossing over shuffles alleles on the same chromosome into new combinations, whereas the random distribution of maternal and paternal chromosomes shuffles alleles on different chromosomes into new combinations.

Question 33

Microscopy to look at a cell’s chromosomes is often done when the cell is in mitotic metaphase. For example, karyotypes that extract chromosomes from a single cell and photograph them to look for abnormalities are done on metaphase, rather than interphase, cells. Why?

Answer 33

In metaphase, chromosomes are condensed and are more easily visualized.

Question 34

List and briefly describe the three major cell cycle checkpoints. For each checkpoint, predict the consequences if the checkpoint failed to work properly.

Answer 34

(1) The G1/S checkpoint holds the cell in G1 until the cell has all of the enzymes necessary for replication of DNA. If the checkpoint failed, the cell would proceed into S without the necessary enzymes, causing the DNA not to be replicated properly or completely. This might cause the cell cycle to halt at the G2/M checkpoint. Alternatively, the cell might divide without the genetic material having been replicated, causing the daughter cells to receive incomplete genetic information. (Both predictions are reasonable based on information in the chapter.) (2) The G2/M checkpoint is passed only if the cell’s DNA is undamaged. If it fails to work properly, division would proceed in the presence of damaged DNA, possibly leading to mutations in the daughter cells and/or death of the daughter cells. (3) The spindle-assembly checkpoint is during metaphase, and it ensures that each chromosome is aligned at the metaphase plate and attached to spindle fibers from opposite poles. This checkpoint depends on tension at the kinetochores of each chromosome. If the checkpoint fails, anaphase will occur even when the chromosomes are not aligned properly, allowing daughter cells to be produced with extra and/or missing chromosomes.

Question 35

Describe what is happening to chromosomes during the five substages of prophase I.

Answer 35

Leptotene – chromosomes contract and become visible Zygotene – chromosomes continue to condense and homologous chromosomes pair up and begin synapsis Pachytene – chromosomes become shorter and thicker, synaptonemal complex develops between homologous chromosomes. Diplotene – centromeres of paired chromosomes move apart – the two homologs remain attached at each chiasma Diakinesis – centromeres have moved apart

Question 36

Describe the difference between the centromere and kinetochore.

Answer 36

A centromere is the physical location on a chromosome where the kinetochore and spindle microtubules attach. The kinetochore is composed of proteins that assemble on the centromere to provide a site for the spindle microtubules to attach.

Question 37

Describe the difference between G1 and G2 of the cell cycle.

Answer 37

G1 occurs before S phase and G2 occurs after S phase. During G1, cells grow in size, chromosomes are composed of a single chromatid. During G1, cells pass a critical checkpoint (the G1/S checkpoint) after which they are committed to undergoing cell division. During G2, the chromosomes are composed of two chromatids. There is another checkpoint during G2 that ensures cells are prepared for mitosis. Cells typically spend more time in G1 than in G2.

Question 38

1. Using the following choices, indicate the correct phase(s) in parts a-e. 1. Meiosis I prophase 2. Meiosis I anaphase 3. Meiosis II prophase 4. Meiosis II anaphase 5. Mitosis prophase 6. Mitosis anaphase a. Chromosomes are in unseparated, sister-chromatid form, at the end of the phase(s) _____. b. The first stage after which a dividing cell that started as a diploid would be haploid. c. Sister chromatids separate during _____. d. Chromosomes are randomly partitioned during _____, contributing to genetic diversity. e. Crossing over (genetic recombination) occurs in _____.

Answer 38

a. 1, 2, 3, 5 b. 2 c. 4, 6 d. 2 e. 1

Question 39

During prophase I of meiosis, crossing over is indicated by what microscopically visible structure?

Answer 39

Chiasmata (chiasma) or the synaptonemal complex

Question 40

What is one feature of meiosis that produces genetic variability in gametes? In two or three sentences, explain how this feature causes genetic uniqueness.

Answer 40

(1) Independent assortment. In meiosis I—metaphase and anaphase—nonhomologous chromosomes distribute randomly. Alignment and separation of one pair of homologous chromosomes is independent of how a different pair separates. Different gametes have different chromosomes can have different alleles for the same genes, so the gametes normally have different combinations of alleles. (2) Crossing over. In meiosis I—prophase—portions of homologous chromosomes exchange, changing combinations of alleles of genes on a single chromosome, so not even sister chromatids are identical after crossing over. Each gamete has only one copy of each homolog, and each homolog now has a unique combination of alleles.

Question 41

List two differences and two similarities between mitosis and meiosis.

Answer 41

Differences: (1) Mitosis occurs in somatic (nonsex) cells; meiosis occurs in sex cells to produce gametes. (2) Meiosis involves chromosome pairing (of homologous chromosomes); mitosis does not. (3) Mitosis produces nonsex cells; meiosis produces gametes. (4) Mitosis produces cells of the same ploidy; meiosis produces haploid cells from diploid cells. (5) Meiosis has two consecutive divisions; mitosis has one. (6) Mitosis produces two daughter cells; meiosis produces four daughter cells. (7) Mitosis produces identical daughter cells; meiosis produces four different daughter cells. Similarities: (1) Both involve the separation of replicated chromosomes during cell division. (2) Both are processes to ensure that daughter cells in cell division receive a complete set of chromosomes. (3) DNA replication must occur first. (4) Cytokinesis usually occurs at the end of each.

Question 42

Describe the difference between meiosis I and meiosis II.

Answer 42

Homologs pair and segregate in meiosis I. Sister chromatids are paired and segregate in meiosis II. Crossing over occurs in meiosis I but not in meiosis II.

Question 43

Describe the difference between the sporophyte and gametophyte.

Answer 43

The sporophyte is the diploid phase of a plant life cycle. The gametophyte is the haploid stage.

Question 44

What events during sexual reproduction are significant in contributing to genetic diversity?

Answer 44

Crossing over changes allele combinations on chromosomes, so, after meiosis I, even sister chromatids are not genetically identical. Independent assortment of non-homologous chromosomes ensures each gamete has a different combination of alleles for genes on non-homologs. Two genetically unique gametes from each parent combine during fertilization to form a novel, genetically unique individual.