Deck 5: Sex Determination and Sex Chromosomes

Question 1

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 1

C

Question 2

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) 1:2 male to female
B) 4:1 male to female
C) 1:1 male to female
D) 2:1 male to female
E) 3:1 male to female

Answer 2

D

Question 3

The Protenor mode of sex determination is the _.

A) scheme based on single translocations in the X chromosome
B) scheme based on F plasmids inserted into the FMR -1 gene
C) XX/XO scheme
D) XO/YY scheme
E) hermaphroditic scheme

Answer 3

C

Question 4

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.

Question 5

In humans, the genetic basis for determining the sex "male" is accomplished by the presence of ________.

A) multiple alleles scattered throughout the autosomes
B) one X chromosome
C) a portion of the Y chromosome
D) a balance between the number of X chromosomes and the number of haploid sets of autosomes
E) high levels of estrogen

Question 6

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 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 their first son will have hemophilia?

A) 3/4
B) 1/8
C) 1/16
D) 1/2
E) 1/4

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

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.

Question 10

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

A) X chromosomes
B) satellited chromosomes
C) chromomeres
D) centromeres
E) Y chromosomes

Question 11

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

Question 12

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)?

Question 13

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) 1/8
B) 1/4
C) 1/16
D) 1/2
E) 3/4

Question 14

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 sons
B) all of his daughters
C) half of his daughters
D) all of his sons
E) all of his children

Question 15

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

Question 16

The Lygaeus mode of sex determination is the _.

A) XX/XO scheme
B) XO/YY scheme
C) XY/XX scheme
D) scheme based on single translocations in the X chromosome
E) hermaphroditic scheme

Question 17

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

A) 47, XYY
B) 47, 21+
C) 47, XXY
D) 45, X
E) triploidy

Question 18

List three abnormalities involving numbers of X chromosomes.

Question 19

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

A) variable
B) one
C) three
D) zero
E) two

Question 20

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 21

What is the composition of a Barr body?

Question 22

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

Question 23

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 24

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 25

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

Question 26

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 27

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

Question 28

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 29

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 30

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

Question 31

Describe three distinct genetic regions of the human Y chromosome.

Question 32

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

Question 33

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

Question 34

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 35

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

Question 36

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?

Question 37

In humans, the male is the homogametic sex.

Question 38

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 39

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.

Question 40

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

Question 41

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

Question 42

Sex -limited genes cause males to be males and females to be females.

Question 43

An individual with Turner syndrome has no Barr bodies.

Question 44

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

Question 45

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

Question 46

A typical XX human female has one Barr body.

Question 47

Sex -influenced genes cause males to be males and females to be females.

Question 48

An individual with Klinefelter syndrome generally has one Barr body.

Question 49

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

Question 50

In Drosophila, the female is the heterogametic sex.