Exam 5: Sex Determination and Sex Chromosomes

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

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

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

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

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

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

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

A typical XX human female has one Barr body.

Describe three distinct genetic regions of the human Y chromosome.

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

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

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 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.

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

List three abnormalities involving numbers of X chromosomes.

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.

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

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.

In humans, the male is the homogametic sex.

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