Exam 7: Sex Determination and Sex Chromosomes

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

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

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.

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

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

What is the composition of a Barr body?

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

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.