Essentials of Genetics 9th Edition By William S. Klug – Test Bank

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Essentials of Genetics, 9e, (Klug et al.)

Chapter 5   Sex Determination and Sex Chromosomes

1) The Protenor mode of sex determination is the ________.

A) scheme based on F plasmids inserted into the FMR-1 gene 

B) XX/XO scheme

C) XO/YY scheme

D) hermaphroditic scheme

E) scheme based on single translocations in the X chromosome 

Answer:  B

Section:  5.1

2) The Lygaeus mode of sex determination is the ________.

A) XY/XX scheme 

B) XX/XO scheme

C) XO/YY scheme

D) hermaphroditic scheme

E) scheme based on single translocations in the X chromosome

Answer:  A

Section:  5.1

3) The sex of birds, some insects, and other organisms is determined by a ZW chromosomal arrangement in which the males have like sex chromosomes (ZZ) and females are ZW (similar to XY in humans). Assume that a recessive lethal allele on the Z chromosome causes death of an embryo in birds. What sex ratio would result in the offspring if a cross were made between a male heterozygous for the lethal allele and a normal female?

A) 4:1 male to female

B) 2:1 male to female 

C) 3:1 male to female

D) 1:2 male to female

E) 1:1 male to female 

Answer:  B

Section:  5.1

4) A recessive gene for red-green color blindness is located on the X chromosome in humans. Assume that a woman with normal vision (her father is color-blind) marries a color-blind male. What is the likelihood that this couple’s first son will be color-blind?

A) 0%

B) 25% 

C) 50%

D) 75%

E) 100%

Answer:  C

Section:  5.2

5) One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. What is the probability that they will have a daughter with hemophilia? (Note: In this problem, you must include the probability of having a daughter in your computation of the final probability.)

A) 1/16

B) 1/8

C) 1/4

D) 1/2

E) 3/4

Answer:  C

Section:  5.2

6) One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. What is the probability that their first son will have hemophilia? 

A) 1/16

B) 1/8

C) 1/4

D) 1/2

E) 3/4

Answer:  D

Section:  5.2

7) In humans, the genetic basis for determining the sex “male” is accomplished by the presence of ________.

A) a portion of the Y chromosome

B) one X chromosome

C) a balance between the number of X chromosomes and the number of haploid sets of autosomes

D) high levels of estrogen 

E) multiple alleles scattered throughout the autosomes

Answer:  A

Section:  5.2

8) Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition? 

A) 47, XXY 

B) 47, 21+

C) 45, X

D) 47, XYY

E) triploidy

Answer:  A

Section:  5.2

9) Assume that a man who carries an X-linked gene has children. Assuming normal meiosis and random combination of gametes, the man would pass this gene to ________.

A) half of his daughters

B) all of his daughters 

C) all of his sons 

D) half of his sons 

E) all of his children

Answer:  B

Section:  5.2

10) For an individual with the XXY chromosomal composition, the expected number of Barr bodies in interphase cells is ________.

A) variable

B) one

C) two

D) three

E) zero

Answer:  B

Section:  5.4

11) In Drosophila, sex is determined by a balance between the number of haploid sets of autosomes and the number of ________. 

A) chromomeres

B) centromeres

C) X chromosomes

D) Y chromosomes

E) satellited chromosomes 

Answer:  C

Section:  5.5

12) Assume that you are told that a particular organism, Drosophila, has the XO chromosome complement. You are also told that the autosomal complement is a normal 2n. You know that in humans the XO complement is female determining. Would you be correct in assuming that the Drosophila sex for XO is also female? Choose the answer that includes the correct explanation.

Answer:  C

Section:  5.5

13) Glucose-6-phosphate dehydrogenase (G6PD) deficiency is inherited as an X-linked recessive gene in humans. A woman whose father suffered from G6PD marries a normal man.

(a) What proportion of their sons is expected to be G6PD?

(b) If the husband were not normal but were G6PD deficient, would you change your answer in part (a)?

Answer:  

(a) 1/2

(b) no

Section:  5.2

14) Below is a pedigree of a fairly common human hereditary trait; the boxes represent males and the circles represent females. Filled-in symbols indicate the abnormal phenotype. Given that one gene pair is involved,

(a) Is the inheritance pattern X-linked or autosomal?

(b) Give the genotype of each individual in the pedigree. If more than one genotypic possibility exists, present all possible alternatives. 

Answer:  

(a) autosomal recessive

(b)

 

Section:  5.3

15) List three abnormalities involving numbers of X chromosomes. 

Answer:  Klinefelter syndrome, Turner syndrome, XXXX syndrome

Section:  5.2

16) Individuals have been identified who have two different karyotypes, such as 45,X/46,XY, or 45,X/46,XX. Such individuals are called ________.

Answer:  mosaics

Section:  5.2

17) What particular karyotype was once considered to be related to criminal predisposition? 

Answer:  XYY

Section:  5.2

18) A small part of the human Y chromosome contains the gene that is responsible for determining maleness. What is the name of this gene?

Answer:  SRY (sex-determining region Y)

Section:  5.2

19) Under what condition might a human female have the XY sex chromosome complement?

Answer:  This female would have one complete X chromosome and a Y chromosome that lacks SRY.

Section:  5.2

20) A color-blind woman with Turner syndrome (XO) has a father who is color-blind. Given that the gene for the color-blind condition is recessive and X-linked, provide a likely explanation for the origin of the color-blind and cytogenetic conditions in the woman. 

Answer:  The woman inherited an Xrg chromosome from the father. Nondisjunction in the female (either at meiosis I or II) produced an egg with no X chromosome, which, when fertilized by the Xrg-bearing sperm, produced the Turner syndrome condition. 

Section:  5.2

21) Although triple-X human females typically have normal offspring, what kinds of gametes, with respect to the X chromosomes, would you expect from such XXX females? Draw meiotic stages that show the gametes that are expected to be produced. 

Answer:  

Section:  5.2

22) How many chromosomes do Klinefelter and Turner syndromes have, respectively?

Answer:  47, 45

Section:  5.2

23) Studies done in the 1960s suggested that individuals with the XYY condition were prone to criminal behavior. What conclusions currently seem appropriate concerning this chromosomal condition?

Answer:  There is a high, but not constant, correlation between the extra Y chromosome and the predisposition of males to have behavioral problems.

Section:  5.2

24) Describe an experiment in which transgenic mice were used to identify the male-determining region of the Y chromosome.

Answer:  When DNA containing only the mouse SRY is injected into normal XX mouse eggs, most of the offspring develop into males.

Section:  5.2

25) Describe three distinct genetic regions of the human Y chromosome.

Answer:  

PARs = pseudoautosomal regions, NRY = nonrecombining region of the Y,
SRY = sex-determining region

Section:  5.2

26) A color-blind, chromatin-positive male child (one Barr body) has a maternal grandfather who was color-blind. The boy’s mother and father are phenotypically normal. Construct and support (using appropriately labeled diagrams) a rationale whereby the chromosomal and genetic attributes of the chromatin-positive male are fully explained. 

Answer:  The female (mother) must be heterozygous and undergo nondisjunction at meiosis II to produce the XrgXrgY boy.

Section:  5.4

27) A cross is made between a female calico cat and a male cat having the gene for black fur on his X chromosome. What fraction of the offspring would one expect to be calico?

Answer:  1/4

Section:  5.4

28) Dosage compensation leads to a variety of interesting coat color patterns in certain mammals. For instance, a female cat that is heterozygous for two coat color alleles, say black and orange, will usually have the “calico” or mosaic phenotype. Describe the chromosomal basis for the mosaicism (calico) in the female. Explain why chromosomally normal male cats do not show the mosaic phenotype, but XXY male cats can be calico.

Answer:  Because of dosage compensation, one of the X chromosomes randomly “turns off” early in development. Once such a chromosome is inactivated, it remains so in daughter cells. Recessive alleles on the remaining active X chromosome are expressed because their normal allele (on the inactive X chromosome) is not capable of expression. Because males typically have only one X chromosome, X chromosome inactivation does not occur; however, in XXY males that are heterozygous for certain coat color genes, such inactivation and mosaicism are possible.

Section:  5.4

29) How many Barr bodies would one expect to see in cells of Turner syndrome females and Klinefelter syndrome males? 

Answer:  zero and one, respectively 

Section:  5.4

30) What can cause phenotypic mosaicism for X-linked genes in female mammals?

Answer:  dosage compensation involving the X chromosome

Section:  5.4

31) Dosage compensation in mammals typically involves the random inactivation of one of the two X chromosomes relatively early in development. Such X chromosome inactivation often leads to phenotypic mosaicism. Assume that black fur in cats is due to the X-linked recessive gene b, whereas its dominant allele B produces yellow fur. A Bb heterozygote is a mosaic called “tortoise shell” or “calico.” Using appropriate gene symbols, diagram a mating between a black male and a calico female. Give the phenotypes and genotypes of all the offspring. 

Answer:  bY× Bb =

Bb (calico female), bb (black female), BY (yellow male), bY (black male)

Section:  5.4

32) What is the composition of a Barr body?

Answer:  X chromosome–associated proteins

Section:  5.4

33) Give the sex-chromosome constitution (X and Y chromosomes) and possible genotypes of offspring resulting from a cross between a white-eyed female (Xw XwY) and a wild-type male (normal chromosome complement) in Drosophila melanogaster. Include all zygotic combinations whether viable or unviable. 

Answer:  

X+XwXw = unviable (dies at third instar stage)

XwXwY = white-eyed female

X+Y = wild-type male

YY = unviable (dies at egg stage)

X+XwY = wild-type female

XwYY = white-eyed male

X+Xw = wild-type female

XwY = white-eyed male

Section:  5.5

34) In Drosophila, an individual female fly was observed to be of the XXY chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The female’s father had red eyes, and the mother had white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, white-eyed individual. It is important that you state in which parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality. 

Answer:  Nondisjunction could have occurred either at meiosis I or meiosis II in the mother, thus giving the XwXwY complement in the offspring.

Section:  5.5

35) In Drosophila, an individual female fly was observed to be of the XXY chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The female’s mother and father had red eyes. The mother, however, was heterozygous for the gene for white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, white-eyed individual. It is important that you state in which parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality.

Answer:  Nondisjunction would have occurred at meiosis II in the mother, thus giving the XwXwY complement in the offspring.

Section:  5.5

36) Give the sex of the following organisms assuming that the autosomes are present in the normal number.

Sex Chromosome Organism

Complement Humans Drosophila

XX________________

XY________________

XO________________

XXX________________

XXY________________

Answer:  

Sex Chromosome Organism

Complement Humans Drosophila

XXfemalefemale

XYmalemale 

XOfemalemale

XXXfemalefemale 

XXYmalefemale

Section:  5.5

37) Assuming a normal number of autosomes, what would be the sex of the following: XXY mouse, XXY Drosophila?

Answer:  male and female, respectively

Section:  5.5

38) Data produced by C. Bridges in the early part of this century indicate that sex in Drosophila is determined by ________.

Answer:  a balance between the number of X chromosomes and the number of haploid sets of autosomes 

Section:  5.5

39) In Drosophila, the sex of a fly with the karyotype XO:2A is ________.

Answer:  male

Section:  5.5

40) True or False: In humans, the male is the homogametic sex.

Answer:  FALSE

Section:  5.1

41) True or False: Normally in humans, all the sons of a male showing a sex-linked phenotype will inherit the trait.

Answer:  FALSE

Section:  5.2

42) True or False: Normally in humans, all the sons of a female homozygous for a sex-linked recessive gene will inherit that trait.

Answer:  TRUE

Section:  5.2

43) True or False: Sex-influenced genes cause males to be males and females to be females.

Answer:  FALSE

Section:  5.2

44) True or False: Sex-limited genes cause males to be males and females to be females.

Answer:  FALSE

Section:  5.2

45) True or False: An individual with Klinefelter syndrome generally has one Barr body.

Answer:  TRUE

Section:  5.4

46) True or False: An individual with Turner syndrome has no Barr bodies.

Answer:  TRUE

Section:  5.4

47) True or False: A typical XX human female has one Barr body.

Answer:  TRUE

Section:  5.4

48) True or False: Dosage compensation is accomplished in humans by inactivation of the Y chromosome.

Answer:  FALSE

Section:  5.4

49) True or False: In Drosophila, the female is the heterogametic sex.

Answer:  FALSE

Section:  5.5

50) True or False: In Drosophila melanogaster, sex is determined by the ratio of the number of X chromosomes to the number of haploid sets of autosomes.

Answer:  TRUE

Section:  5.5