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Exam 5: Sex Determination and Sex Chromosomes

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Question 21

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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%

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Question 22

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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

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Question 23

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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.

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

Describe three distinct genetic regions of the human Y chromosome.

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

List three abnormalities involving numbers of X chromosomes.

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.

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.

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

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 typical XX human female has one Barr body.

The Lygaeus mode of sex determination is the ________.

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

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.

In humans,the male is the homogametic sex.

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

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

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

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