9
Chromosomes, the Cell Cycle, and Cell Division
TEST FILE QUESTIONS
Fill in the Blank
1. When a DNA molecule doubles, a chromosome is then made up of two joined
_______.
Answer: chromatids
2. Prokaryotic DNA molecules are packaged by _______ proteins, which associate with
DNA.
Answer: basic
3. In general, the division of the cell, called _______, follows immediately upon mitosis.
Answer: cytokinesis
4. Bacteria have a short sequence called _______, where DNA synthesis begins.
Answer: ori
5. Bacteria have a short sequence called _______, where DNA synthesis ends.
Answer: ter
6. During prophase I of meiosis, a unique event occurs that results in the formation of
recombinant chromosomes. This event is termed _______.
Answer: crossing over
7. The structure present during mitosis that is composed of two identical DNA molecules
complexed with proteins and joined at the centromere is called a _______.
Answer: chromosome
8. The stage of the cell cycle during which DNA replicates is called the _______.
Answer: S phase
9. _______ is the fusion of two gametes.
Answer: Fertilization
10. During prometaphase, the chromatids are held together by _______.
Answer: cohesion
11. Occasionally, a homologous chromosome pair fails to separate during anaphase I of
meiosis. One of the resulting cells lacks a copy of this chromosome, whereas the other
contains both members of the homologous pair. These cells are called _______ cells.
Answer: aneuploid
12. During a process known as _______, a piece of
become joined to a different chromosome.
Answer: translocation
13. The orderly distribution of genetic information occurs in prokaryotic cells by a
process known as _______.
Answer: fission
14. A cell with three homologous sets of chromosomes is called a _______ cell.
Answer: triploid
15. The heritable information of the cell is _______.
Answer: DNA
16. The process that ensures that genetic information is passed on to a cell’s daughter
cells is _______.
Answer: mitosis
17. The process that ensures that only one of each pair of chromosomes is included in a
gamete is _______.
Answer: meiosis
18. The main role of nucleosomes in eukaryotic cells is to _______ the DNA.
Answer: package
19. The G2 phase always follows _______ phase.
Answer: S
20. The G in G1 and G2 is short for _______.
Answer: gap
21. The chromatin _______ during prophase.
Answer: condenses
22. The milestone event that defines entry into prometaphase is _______.
Answer: loss of the nuclear envelope
23. In plants, a _______ forms at the equatorial region of the cell.
Answer: cell plate
24. The cell plate is derived from the _______ of the cell.
Answer: Golgi apparatus
25. The “invisible thread” that pinches cells apart during cell division is made of _______
and _______.
Answer: actin; myosin
26. A zygote usually has _______ copies of each chromosome.
Answer: two
27. The _______ is the number, form, and type of chromosomes found in a cell.
Answer: karyotype
28. A _______ is one of a pair of chromosomes having the same overall genetic
composition and sequence.
Answer: homolog
29. Nondisjunction causes the production of _______ cells.
Answer: aneuploid
30. Down syndrome can be caused by an extra chromosome _______.
Answer: 21
STUDY GUIDE QUESTIONS
Knowledge and Synthesis Questions
1. Which of the following is true of mitosis?
a. The chromosome number in the resulting cells is halved.
b. DNA replication is completed prior to the beginning of this phase.
c. The chromosome number of the resulting cells is the same as that of the parent cell.
d. Both b and c
2. Which of the following is true of meiosis?
a. The chromosome number in the resulting cells is halved.
b. DNA replication occurs after the beginning of this phase.
c. The homologs do not pair during prophase I.
d. The chromosome number of the resulting cells is the same as that of the parent cell.
3. Which of the following is true of kinetochores?
a. They are located at the centromere of each chromosome.
b. They are the sites where microtubules attach to separate the chromosomes.
c. They are organized so that there is one per sister chromatid.
d. All of the above
4. Which of the following is true of the mitotic spindle?
a. It is composed of actin and myosin microfilaments.
b. It is composed of kinetochores at the metaphase plate.
c. It is composed of microtubules, which help separate the chromosomes to opposite
poles of the cell.
d. It originates only at the centrioles in the centrosomes.
5. Imagine that there is a mutation in the Cdk2 gene such that its gene product is
nonfunctional. What kind of effect would this mutation have on a mature red blood cell?
a. The cell would be unable to replicate its DNA.
b. The cell would not be able to enter G1.
c. The cell would be unable to reproduce itself.
d. There would be no effect, because mature red blood cells do not enter the cell cycle.
6. Imagine that there is a mutation in the Cdk2 gene such that its gene product is
nonfunctional. What kind of effect would this mutation have on a cell at the tip of a
plant’s root?
a. The cell would be unable to replicate its DNA.
b. The cell would be unable to enter G1.
c. The cell would be unable to reproduce itself.
d. Both a and c
7. Which is true of DNA replication and cytokinesis in Escherichia coli?
a. DNA replication occurs in the nucleus.
b. Cytokinesis is facilitated by microfilaments of myosin and actin.
c. Cell reproduction is initiated by reproductive signals, which result in DNA replication,
DNA segregation, and cytokinesis.
d. The E. coli chromosome is linear.
8. Which of the following is true of chromatids?
a. They are replicated chromosomes still joined together at the centromere.
b. They are identical in mitotic chromosomes.
c. They are identical in meiotic chromosomes.
d. Both a and b
9. Histones are positively charged because
a. the majority of the ions in the nucleus of the cell are negatively charged.
b. histones interact with acidic residues of proteins found in the nucleus.
c. the basic side chains of histone proteins interact with the negatively charged DNA.
d. histones have a majority of acidic residues in their protein sequence.
10. Chromosome movement during anaphase is the result of
a. the molecular motors at the kinetochores that move the chromosomes toward the poles.
b. molecular motors at the centrosome that pull the microtubules toward the poles.
c. shortening of the microtubules at the centrosome that pull the chromosomes toward the
poles.
d. Both a and c
11. Programmed cell death (apoptosis)
a. occurs in cells that have been deprived of essential nutrients.
b. occurs only in cells that have damaged DNA.
c. is a natural process during development.
d. is signaled by the initiation of mitosis.
Answers to Questions
Knowledge and Synthesis Answers
1. d. Mitosis occurs after DNA replication and results in cells having the same number of
chromosomes as the parent cell.
2. a. Meiosis occurs after one round of DNA replication. Homologous chromosomes pair
during prophase I of meiosis, and the resulting cells have half the number of
chromosomes as the parent cell.
3. d. Kinetochores, one per sister chromatid, are assembled at the centromere of each
chromosome and are the sites in which microtubules attach to segregate the
chromosomes.
4. c. The mitotic spindle is composed of microtubules, not actin and myosin filaments.
The spindle originates from the centrosome, which may or may not have centrioles.
5. d. Many cells, such as red blood cells, muscle cells, and nerve cells, lose their ability to
divide as they mature.
6. d. A cell at the tip of a plant’s root needs to be able to divide to contribute to the
growth of the root. Dividing cells do enter the cell cycle, and cyclin-Cdk complexes
signal transitions in the cell cycle. The cyclin E-Cdk2 complex acts in the middle of G1,
and the cyclin A-Cdk2 complex acts in S1 and stimulates DNA replication. Without
functional Cdk2, no catalytically active cyclin-Cdk complexes can form. The cell will be
unable to replicate its DNA and will not progress through the cell cycle to reproduce
itself.
7. c. Escherichia coli is a prokaryote and lacks a nucleus, has a circular chromosome, and
does not synthesize actin or myosin proteins. Cytokinesis in E. coli is a result of a
reproductive signal that causes the DNA to be replicated and segregated, and finally
causes the cell to divide.
8. d. Chromatids are highly condensed, newly replicated chromosomes, which will be
segregated to the daughter cells. After DNA replication, chromatids are still attached to
one another at the centromere. Meiotic sister chromatids are different from one another
due to crossing over in prophase of meiosis I. Mitotic sister chromatids are identical.
9. c. The positive charges on histone proteins are due to the large number of basic amino
acid residues found in these proteins. These positive charges interact with the negatively
charged phosphate sugar backbone of DNA during assembly of the DNA on the
nucleosome.
10. d. Chromosomes are attached to the microtubules at their kinetochores. There are
molecular motors at the kinetochores, which help move the chromosomes to opposite
poles. Chromosomes are also pulled toward the poles by the shortening of the
kinetochore microtubules.
11. c. Programmed cell death occurs during the development of many organisms (for
instance, tadpoles lose their tails to become adult frogs). One of the stimuli for
programmed cell death is DNA damage, but it is not the only cause of death. Necrosis
(cell death that is not programmed) occurs when cells have been deprived of essential
nutrients. The initiation of mitosis is part of the cell cycle, in which cells reproduce, and
is not a step in programmed cell death.
10
Genetics: Mendel and Beyond
TEST FILE QUESTIONS
Fill in the Blank
1. A _______ trait is one that can be passed from one generation to another.
Answer: heritable
2. A _______ is a portion of DNA that resides at a particular locus or site on a
chromosome and encodes a particular function.
Answer: gene
3. To determine the overall probability of independent events, _______ the probabilities
of the individual events.
Answer: multiply
4. One particular allele of a gene may be defined as _______ or standard, because it is
present in most individuals and gives rise to an expected trait, or phenotype.
Answer: wild type
5. Geneticists make use of _______ frequencies to map chromosomes, that is, to locate
genetic loci on the chromosome.
Answer: recombinant
6. A cross between two parents that differs by a single trait is a _______ cross.
Answer: monohybrid
7. The physical appearance of a character is the _______, whereas the genetic
constitution is the _______.
Answer: phenotype; genotype
8. A cross between two heterozygous parents that differs by two independent traits is a
_______ cross.
Answer: dihybrid
9. Genes at different loci on the same chromosome can separate and recombine to form
_______.
Answer: recombinant chromosomes
10. The region of the chromosome occupied by a gene is called a _______.
Answer: locus
11. When a cross is made and a trait disappears in the F1 generation, only to reappear in
the F2, the trait is probably _______.
Answer: recessive
12. A female who is heterozygous for a recessive sex-linked character is a _______.
Answer: carrier
13. When the expression of one gene depends on the expression of another gene, the
genes demonstrate _______.
Answer: epistasis
14. When many genes contribute to the phenotype, variation is said to be _______.
Answer: continuous
15. A _______ is an observable feature, such as flower color; a _______ is a particular
form of a character, such as a white flower.
Answer: character; trait
16. The AB phenotype found in individuals with IAIB genotype is an example of _______.
Answer: codominance
17. To determine the probability of an event that can occur in two or more different ways,
_______ the individual probabilities.
Answer: add
18. Quantitative variation is the result of the interaction of _______ and _______.
Answer: genes; environment
19. Mendel’s laws of inheritance can be applied to human genetics through the study of
_______.
Answer: pedigrees
20. Recombination is most likely between two loci that are _______.
Answer: far apart
STUDY GUIDE QUESTIONS
Knowledge and Synthesis Questions
1. In the beginning of Chapter 10, hemophilia is mentioned as a trait carried by the
mother and passed to her sons. What is the pattern of inheritance for this trait?
a. Hemophilia is an allele carried on one of the mother’s autosomal chromosomes.
b. Hemophilia is an allele carried on the Y chromosome because more males have this
genetic disorder than females.
c. Hemophilia is an allele carried on the X chromosome and can be directly inherited by
the son from the father or the mother.
d. Hemophilia is carried on the X chromosome and can only be inherited by the son if the
mother is a carrier.
2. Originally, genetic inheritance was thought to be a function of the blending of traits
from the two parents. Which exception to Mendel’s rules is an example of blending?
a. Polygenic inheritance
b. Incomplete dominance
c. Codominance
d. Pleiotropism
3. True-breeding plants
a. produce the same offspring when crossed for many generations.
b. result from a monohybrid cross.
c. result from a dihybrid cross.
d. result from crossing over during prophase I of meiosis.
4. What is the probability that a cross between a true- breeding pea plant with spherical
seeds and a true- breeding pea plant with wrinkled seeds will produce F1 progeny with
spherical seeds?
a. 1/2
b. 1/4
c. 0
d. 1
5. What is the pattern of inheritance for a rare recessive allele?
a. Every affected person has an affected parent.
b. Unaffected parents can produce children who are affected.
c. Unaffected mothers have affected sons and daughters who are carriers.
d. None of the above
6. What is the pattern of inheritance for a rare dominant allele?
a. Every affected person has an affected parent.
b. Unaffected parents can produce children who are affected.
c. Unaffected mothers have affected sons and daughters who are carriers.
d. None of the above
7. What is the pattern of inheritance for a sex-linked allele?
a. Every affected person has an affected parent.
b. Unaffected parents can produce children who are affected.
c. Unaffected mothers have affected sons and daughters who are carriers.
d. None of the above
8. Penetrance and expressivity are related to
a. the increased expression of a particular trait when a hybrid species is formed.
b. quantitative traits that diminish or intensify a particular phenotype.
c. the influence of environment on the expression of a particular genotype.
d. the expression of one gene masking the effects of another gene.
9. Sex determination in grasshoppers, humans, and Drosophila is similar because
a. females are hemizygous.
b. males have one X chromosome and females have two X chromosomes.
c. all males always have one Y chromosome in all three species.
d. the ratio of X chromosomes to sets of autosomes determines maleness or femaleness.
10. Linked genes are genes that
a. assort independently.
b. segregate equally in the gametes during meiosis.
c. always contribute the same trait to the zygote.
d. are found on the same chromosome.
e. recombine during mitosis.
11. Cytoplasmic inheritance
a. results from polygenic nuclear traits.
b. is the result of gametes contributing equal amounts of cytoplasm to the zygote.
c. is determined by genes on DNA molecules in mitochondria and chloroplasts.
d. follows Mendel’s law of segregation.
Answers to Questions
Knowledge and Synthesis Answers
1. d. Hemophilia is an X-linked trait and can only be inherited by the son from his
mother’s X chromosome. The father contributes the Y chromosome to his son (not his X
chromosome) and thus cannot pass any of his X-linked alleles to his son.
2. b. Incomplete dominance results in the progeny’s expressing an intermediate form of
the two parental alleles. (In a cross between red-flowered plants and white-flowered
plants, the expression of pink-flowered plants would be a “blend” of the parental traits.)
Codominance is not an example of blending because both alleles are fully expressed in
the individual.
3. a. Monohybrid and dihybrid crosses produce heterozygous individuals; true-breeding
individuals are always homozygous.
4. d. This is an example of a monohybrid cross. All of the F1 progeny would have
spherical seeds. (The F1 generation would all have the genotype Ss, producing the
phenotype of spherical seeds because the spherical allele, S, is dominant to the wrinkled
allele, s.)
5. b. Rare recessive alleles can be carried by both parents but not expressed in those
parents. The parents will be heterozygous for this allele (Aa). Their children will have a
one-fourth probability of expressing that recessive allele (aa).
6. a. If an allele is dominant, every affected individual has at least one dominant allele.
An affected individual must have received that allele from one of his or her parents.
Because the allele is dominant, that parent must also be affected.
7. c. The most common sex-linked alleles are X-linked and are passed from a mother to
her son (because the mother always donates one of her X chromosomes to her son and the
father always donates the Y chromosome to his son). Daughters can also receive the Xlinked allele from their mothers, but the father donates the other X chromosome, so
daughters can be carriers.
8. c. Penetrance and expressivity are related to the effects the environment has on a
particular phenotype. Answer a refers to hybrid vigor, answer b refers to quantitative
traits, and answer d refers to epistasis.
9. b. In these three species, females have two X chromosomes and males have one X
chromosome. The ratio of X chromosomes to autosome sets is important for sex
determination in Drosophila, but not in grasshoppers or humans. In Drosophila male flies
can be XO (they are normally XY) and female flies can be XXY (they are normally XX).
10. d. Linked genes by definition are on the same chromosome and thus do not assort
independently, do not contribute the same trait to the zygote, and do not recombine
during mitosis or segregate equally to the gametes during meiosis.
11. c. The genes on the mitochondria and chloroplast chromosomes are passed on to all
of the progeny from the gamete that contributes the majority of the cytoplasm.