Deck 7: Sex Determination and Sex Chromosomes

Question 1

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 1

A

Question 2

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 2

(a) 1/2 (b) no

Question 3

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 3

B

Question 4

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

Question 5

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.

Question 6

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

Question 7

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

Question 8

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

Question 9

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

Question 10

What particular karyotype was at one time considered to be related to criminal predisposition?

Question 11

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

A) telomeres
B) centromeres
C) X chromosomes
D) Y chromosomes
E) nucleolar organizers

Question 12

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

Question 13

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

Question 14

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

Question 15

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%

Question 16

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

Question 17

List three abnormalities involving numbers of X chromosomes.

Question 18

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.

Question 19

The accompanying figure 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.

Question 20

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.

A) Yes, because sex determination in humans and insects is essentially the same.
B) No, sex determination in Drosophila is dependent on the presence or absence of the Y chromosome.
C) No, the chromosomal basis for sex determination in Drosophila is based on the balance between the number of X chromosomes and haploid sets of autosomes.
D) Yes, the presence of an X chromosome determines a female in both organisms.
E) No, it takes two X chromosomes to produce a female in humans and a Y chromosome to produce a male in Drosophila.

Question 21

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

Question 22

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.

Question 23

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

Question 24

Klinefelter and Turner syndromes have how many chromosomes, respectively?

Question 25

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

Question 26

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

Question 27

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

Question 28

Normally in humans, all the sons of a male showing a sex-linked phenotype will inherit the trait.

Question 29

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

Question 30

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.

Question 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.

Question 32

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.

Question 33

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?

Question 34

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

Question 35

Describe three distinct genetic regions of the human Y chromosome.

Question 36

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

Question 37

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

Question 38

In humans, the male is the homogametic sex.

Question 39

What is the composition of a Barr body?

Question 40

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.

Question 41

Dosage compensation is accomplished in humans by inactivation of the Y chromosome.

Question 42

A typical XX human female has one Barr body.

Question 43

An individual with Klinefelter syndrome generally has one Barr body.

Question 44

An individual with Turner Syndrome has no Barr bodies.

Question 45

In Drosophila, sex is determined by the ratio of the number of X chromosomes to the number of haploid sets of autosomes.

Question 46

Normally in humans, all the sons of a female homozygous for a sex-linked recessive gene will inherit that trait.

Question 47

In Drosophila, the female is the heterogametic sex.