Chapter 4

Question 1

What is the role of the SRY gene in humans?

a. It initiates the X inactivation process in females.
b. It is located on the X chromosome and causes the X to pair with the Y chromosome during male meiosis.
c. It is located on the Y chromosome and initiates the developmental pathway toward the male phenotype.
d. It is located on an autosomal chromosome and represses expression of autosomal genes in order to balance their expression level with genes on the X chromosome.
e. None of the above answers is correct.

Answer 1

c. It is located on the Y chromosome and initiates the developmental pathway toward the male phenotype.

Question 2

What is the expected outcome for a human embryo with the XXXY chromosome constitution?

a. It would likely develop into a female who will not respond to the hormone testosterone.
b. It would likely develop into a sterile male with reduced testes.
c. It will always abort early in development before birth.
d. It would likely develop into a tall female who may be slightly cognitively impaired.
e. It would likely develop into a fertile man with a completely normal male phenotype.

Answer 2

b. It would likely develop into a sterile male with reduced testes.

Question 3

Which of the following chromosome constitutions would never lead to a viable human baby being born?

a. XXX
b. XYY
c. XO (O = the absence of a second chromosome)
d. YY
e. XXY

Answer 3

d. YY

Question 4

A female with androgen-insensitivity syndrome, a sex-linked recessive condition, has

a. two X chromosomes, both carrying mutant alleles in the gene that makes the androgen receptor.
b. a pair of ovaries that overproduce estrogen.
c. a XXX chromosome constitution that causes her not to produce testosterone.
d. a pair of testes that produce testosterone.
e. an inactive SRY gene.

Answer 4

d. a pair of testes that produce testosterone.

Question 5

Species in which individuals have only male or only female reproductive structures are called

a. hermaphrodites.
b. diploids.
c. dioecious.
d. homogametic.
e. monoecious.

Answer 5

c. dioecious.

Question 6

In which of the following organisms is gender/sex determined by the temperature during embryonic development?

a. Humans
b. Mice
c. Fruit flies
d. Many snakes and birds
e. Many turtles and alligators

Answer 6

e. Many turtles and alligators

Question 7

In species of birds, males are the homogametic sex and females the heterogametic sex. Which if the following is true in this system of sex determination?

a. The gender of the offspring is determined by the female parent.
b. Male offspring have a ZW chromosome constitution.
c. The gender of the offspring is determined by the male parent.
d. Female offspring have a ZZ chromosome constitution.
e. Female and male offspring have the same chromosome constitution.

Answer 7

a. The gender of the offspring is determined by the female parent.

Question 8

In a germ-line cell from a female grasshopper (XX-XO sex determination system), when do the homologous X chromosomes segregate?

a. During mitosis
b. During meiosis I, anaphase
c. During meiosis II, anaphase
d. They do not segregate; gametes contain a copy of X and a copy of Y.

Answer 8

b. During meiosis I, anaphase

Question 9

In a germ-line cell from a human male that is dividing, when do the X and Y chromosomes segregate?

a. During mitosis
b. During meiosis I, anaphase
c. During meiosis II, anaphase
d. They do not segregate; gametes contain a copy of X and a copy of Y.

Answer 9

b. During meiosis I, anaphase

Question 10

Which of the following human genotypes is associated with Klinefelter syndrome?

a. XXY
b. XXXY
c. XXXXY
d. All of the above
e. None of the above

Answer 10

d. All of the above

Question 11

What is the sex chromosome constitution of a male duck-billed platypus?

a. XX
b. XY
c. XO
d. ZZ
e. XXXXXYYYYY

Answer 11

e. XXXXXYYYYY

Question 12

An XXY chromosome constitution produces ________ development in humans and _________ development in fruit flies.

a. female; female
b. male; male
c. female; male
d. male; female
e. male, intersex

Answer 12

d. male; female

Question 13

The sex determination system used by Drosophila is called

a. the X:A sex determination system.
b. the ZZ-ZW sex determination system.
c. the XX-XO sex determination system.
d. the XX-XY sex determination system.
e. Both b and c are correct.

Answer 13

a. the X:A sex determination system.

Question 14

With the XX-XO sex determination system, generally

a. female offspring have one X chromosome, and it is inherited from their father.
b. male offspring have one X chromosome, and it is inherited from their mother.
c. male offspring have one X chromosome, and it is inherited from their father.
d. female offspring have one X chromosome, and it is inherited from their mother.
e. None of the above statements is true.

Answer 14

b. male offspring have one X chromosome, and it is inherited from their mother.

Question 15

Species in which an individual organism has both male and female reproductive structures are called

a. monoecious.
b. haploid.
c. diploid.
d. dioecious.
e. Both c and d are correct.

Answer 15

a. monoecious.

Question 16

Human females with XY chromosomes and a phenotype that includes the absence of a uterus and ovaries and the presence of testes are likely to have which of the following mutations?

a. A mutation in the SRY gene
b. A mutation in the androgen receptor gene
c. A deletion that removes much of the Y chromosome
d. They likely do not carry a mutation but may have been premature babies.
e. None of the above answers is correct.

Answer 16

b. A mutation in the androgen receptor gene

Question 17

Human males, with XY chromosomes are___________ and produce two different kinds of gametes, whereas females with XX chromosomes are ___________ and produce only one kind.

a. homogametic; heterogametic
b. dioecious; monoecious
c. heterogametic; homogametic
d. monoecious; dioecious
e. monoecious; heterogametic

Answer 17

c. heterogametic; homogametic

Question 18

In which of the following phenotypic females do testes develop?

a. XY with an deletion that removes the SRY gene
b. XO
c. XY with the X-linked recessive condition of androgen insensitivity syndrome
d. XX
e. Both a and b are correct.

Answer 18

c. XY with the X-linked recessive condition of androgen insensitivity syndrome

Question 19

During the evolution of the human Y chromosome, all of the following are assumed to occur except

a. the original chromosome was an autosome that eventually evolved into the Y chromosome.
b. one of the early events in the evolution of the Y chromosome was the acquisition or evolution of a gene somewhat similar to the current human SRY gene.
c. many of the genes on the original ancestral chromosome suffered mutations and became inactive during the evolution of the Y chromosome.
d. many of the genes on the early X chromosome that were responsible for critical cellular functions got moved to the evolving Y chromosome.
e. several palindromic regions evolved or were acquired and are now present on the Y chromosome.

Answer 19

d. many of the genes on the early X chromosome that were responsible for critical cellular functions got moved to the evolving Y chromosome.

Question 20

Red-green color blindness is X-linked recessive. A woman with normal color vision has a father who is color blind. The woman has a child with a man with normal color vision.Which phenotype is NOT expected?

a. A color-blind female
b. A color-blind male
c. A noncolor-blind female
d. A noncolor-blind male

Answer 20

a. A color-blind female

Question 21

Which statement best summarizes our current understanding of the origin of the Y chromosome?

a. The Y chromosome is thought to have arisen spontaneously in an ancestor of mammals millions of years ago.
b. The Y chromosome is thought to have arisen as a fusion of two autosomes.
c. The Y chromosome is thought to have arisen as a broken fragment of the X chromosome.
d. The Y chromosome is thought to have been derived along with the X chromosome from a pair of autosomes.
e. Both a and c are correct.

Answer 21

d. The Y chromosome is thought to have been derived along with the X chromosome from a pair of autosomes.

Question 22

If a female Drosophila that is heterozygous for a recessive X-linked mutation is crossed to a wild-type male, what proportion of female progeny will have the mutant phenotype?

a. 100%
b. 0%
c. 33%
d. 25%

Answer 22

b. 0%

Question 23

A woman is phenotypically normal, but her father had the sex-linked recessive condition of red-green colorblindness. If she has children with a man with normal vision, what is the probability that their first child will have normal vision and their second child will be colorblind?

a. 1/16
b. 3/8
c. 3/16
d. 3/6
e. 8/27

Answer 23

c. 3/16

Question 24

A eukaryotic diploid cell from an organism with the ZZ-ZW sex determination system has two pairs of autosomes and a pair of sex chromosomes, Z and W, shown below. What kind of individual is this?

a. Male
b. Female
c. Hermaphrodite
d. Monoecious

Answer 24

b. Female

Question 25

A eukaryotic diploid cell from an organism with the ZZ-ZW sex determination system has two pairs of autosomes and a pair of sex chromosomes, Z and W, shown below. A diploid cell from this individual begins to go through meiosis. After the completion of meiosis I, it becomes two cells. One of these two cells now undergoes meiosis II. Which of the following is a possible normal combination of chromosomes in one of the subsequent two cells after the completion of meiosis II? a. One chromosome with the A allele, one with the B allele, one Z, one W b. One chromosome with the A allele, one with the a allele, one with the B allele, one with the b allele, one Z, one W c. A pair of chromosomes with A alleles, a pair of chromosomes with B alleles, a pair of Z chromosomes d. One chromosome with an a allele, one chromosome with a B allele, one W e. Both c and c are possible.

Answer 25

d. One chromosome with an a allele, one chromosome with a B allele, one W

Question 26

A eukaryotic diploid cell from an organism with the ZZ-ZW sex determination system has two pairs of autosomes and a pair of sex chromosomes, Z and W, shown below. What is the probability of a gamete from this individual that has the following genotype: alleles A and b, chromosome Z? a. 1/2 b. 1/4 c. 1/6 d. 1/8 e. 1/16

Answer 26

d. 1/8

Question 27

A eukaryotic diploid cell from an organism with the ZZ-ZW sex determination system has two pairs of autosomes and a pair of sex chromosomes, Z and W, shown below. Assume A and B are dominant alleles. If this individual were crossed to an individual of genotype Aa Bb, what is the probability of a female offspring with the two dominant traits given by alleles A and B? a. 1/8 b. 1/16 c. 9/16 d. 9/32 e. 3/32

Answer 27

d. 9/32

Question 28

A eukaryotic diploid cell from an organism with the XX-XO sex determination system has two pairs of autosomes and one X chromosome, shown below. From what type of individual is this cell? a. Male b. Female c. Hermaphrodite d. Monoecious e. Intersex

Answer 28

a. Male

Question 29

A eukaryotic diploid cell from an organism with the XX-XO sex determination system has two pairs of autosomes and one X chromosome, shown below. A diploid cell from this individual begins to go through meiosis. After the completion of meiosis I, it becomes two cells. One of these two cells now undergoes meiosis II. Which of the following is a possible normal combination of chromosomes in one of the subsequent two cells after the completion of meiosis II? a. One chromosome with the A allele, one with the B allele, and two X chromosomes b. One chromosome with the A allele, one with the a allele, one with B allele, one with b allele, and two X chromosomes c. One chromosome with the A allele, one chromosome with the B allele d. One chromosome with the a allele, one chromosome with the B allele, one X chromosome e. Both c and d are possible.

Answer 29

e. Both c and d are possible.

Question 30

A eukaryotic diploid cell from an organism with the XX-XO sex determination system has two pairs of autosomes and one X chromosome, shown below. What is the probability of a gamete from this individual that has the following genotype: alleles A and b, chromosome X? a. 1/2 b. 1/4 c. 1/6 d. 1/8 e. 1/16

Answer 30

d. 1/8

Question 31

If a male bird that is heterozygous for a recessive Z-linked mutation is crossed to a wild type female, what proportion of the progeny will be mutant males? a. 0% b. 100% c. 75% d. 50% e. 25%

Answer 31

a. 0%

Question 32

A woman has normal vision although her maternal grandfather (her mother’s father) had red-green colorblindness, a sex-linked recessive trait. Her maternal grandmother and the woman’s own father are assumed to not possess a copy of the mutant allele. The woman marries a man with normal vision although his father was colorblind. What is the probability that the first child of this couple will be colorblind? a. 1/2 b. 1/4 c. 1/8 d. 1/16 e. 1/12

Answer 32

c. 1/8

Question 33

Joan is phenotypically normal, but had a child with the autosomal recessive disease cystic fibrosis (CF) from a previous marriage. Joan’s father has hemophila A, a sex-linked recessive condition where the blood fails to clot properly. Her father has survived due to recent treatment advances. Joan now intends to marry Bill, who is also phenotypically normal but who has a sister, Jill, with CF. Bill’s parents are phenotypically normal, and there is no history of hemophilia A in his family. Assume that Joan and Bill do marry and have a child. What is the probability that this child will have CF, but will not have hemophilia A ? (Hint: This problem requires that you utilize concepts from Chapter 3 as well as Chapter 4.) a. 1/8 b. 1/12 c. 1/24 d. 3/32 e. 5/32

Answer 33

a. 1/8

Question 34

In humans there is a genetic disorder that results from a dominant mutation present in a gene located in the pseudoautosomal region of the Y chromosome and on the X chromosome.Which of the following statements is correct? a. All affected men marrying normal women will have no affected daughters. b. All affected women marrying normal men will have affected daughters and no affected sons. c. All affected men marrying normal women will have affected daughers, but all the sons will be normal. d. All affected women marrying nomal men will have only normal sons and daughters. None of the above statements is correct.

Answer 34

e. none are correct.

Question 35

Familial vitamin-D-resistant rickets is an X-linked dominant condition in humans. If a man is afflicted with this condition and his wife is normal, it is expected that among their children, all the daughters would be affected and all the sons would be normal. In families where the husband is affected and the wife is normal, this is almost always that outcome among their children when such families have been studied. Very rarely an unexpected result occurs in such families where a boy is born with the disorder. If the chromosomes of such unusual boys are examined, what might be expected to be found? a. Some of the boys are XYY. b. Some of the boys are XY but have lost the SRY gene from their Y chromosome. c. Some of the boys are YY. d. Some of the boys are XXY. e. Some of the boys are XXX.

Answer 35

d. Some of the boys are XXY.

Question 36

A Barr body is a(n): a. gene on the X chromosome that is responsible for female development. b. patch of cells that has a phenotype different from surrounding cells because of variable X inactivation. c. inactivated X chromosome, visible in the nucleus of a cell that is normally from a female mammal. d. extra X chromosome in a cell that is the result of nondisjunction. extra Y chromosome in a cell that is the result of nondisjunction

Answer 36

c. inactivated X chromosome, visible in the nucleus of a cell that is normally from a female mammal.

Question 37

Which of the following statements about X inactivation in mammalian females is false? a. Females that are heterozygous for an X-linked gene have patches of cells that express one allele and patches of cells that express the other. b. Some genes on the inactive X continue to be expressed after the chromosome is inactivated. c. X inactivation is random as to which X is inactivated and takes place early in embryonic development d. Inactivation is thought to be initiated by expression of the Xist gene on the X that will remain active. e. Once an X chromosome first becomes inactivated in a cell, that same X will remain inactivated in somatic cells that are descendants of this cell.

Answer 37

d. Inactivation is thought to be initiated by expression of the Xist gene on the X that will remain active.

Question 38

What is the apparent purpose for X inactivation in humans and other mammals? a. It allows for the levels of expression of genes on the X chromosome to be similar in males and females. b. It allows for the levels of expression of genes on the autosomes to be similar to the levels of genes on the X chromosome. c. It suppresses the expression of genes on the Y chromosome in males. d. It reduces the amount of nondisjunction during meiosis in females. e. It enhances the level of pairing between the two X chromosomes during meiosis in females.

Answer 38

a. It allows for the levels of expression of genes on the X chromosome to be similar in males and females.

Question 39

The Lyon hypothesis helps us to understand which phenomenon in mammals? a. X-linked inheritance b. Evolution of the Y chromosome c. Dosage compensation between males and females d. Development of male and female secondary sexual characteristics e. Sex determination

Answer 39

c. Dosage compensation between males and females

Question 40

Women with Turner syndrome (XO) and normal women (XX) are clearly different phenotypically. In addition, the vast majority of XO conceptions abort before birth. However, both XO and XX women have one active X chromosome since the X in XO women remains active and one might expect that they would therefore have similar phenotypes. What is the most reasonable explanation for their different phenotypes? a. XO women do not have a copy of the SRY gene. b. Some genes remain active on the inactive X chromosome and XX women will have two copies of these genes expressed and XO women only one copy. c. In XO women, the single X chromosome has no partner to pair with during mitosis so that each cell division is delayed by pairing problems with the single X not finding a pairing partner. d. XO women are missing a copy of the XIST gene so that they are forced to develop partway along the male pathway during embryogenesis. e. Both c and d are reasonable explanations.

Answer 40

b. Some genes remain active on the inactive X chromosome and XX women will have two copies of these genes expressed and XO women only one copy.

Question 41

In which of the following individuals would you expect to find two Barr bodies in their somatic cells? a. XX b. XO c. XXY d. XXYY e. XXX

Answer 41

e. XXX

Question 42

Normal males (XY) and Klinefelter males (XXY) both possess only one active X chromosome. Nonetheless there are clearly phenotypic differences between the two. What is the most reasonable explanation as to why such differences exist? a. The Y chromosome has higher gene expression levels when two X chromosomes are present compared to one X. b. The Y chromosome has lower gene expression levels when two X chromosomes are present compare to one X. c. Some genes remain active on inactive X chromosomes so XXY males would produce have higher expression levels for these genes compared to XY males. d. XXY males exhibit a higher rate of problems during mitotic divisions than XY males. e. XXY males don’t have a copy of the SRY gene.

Answer 42

c. Some genes remain active on inactive X chromosomes so XXY males would produce have higher expression levels for these genes compared to XY males.

Question 43

How many Barr bodies (condensed X chromosomes) would you predict in this boy’s cells? a. One per somatic cell b. Two per somatic cell c. Three per somatic cell d. None e. Either two or three depending on the tissue type

Answer 43

a. One per somatic cell