Exam 5: Sex Determination and Sex Chromosomes

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

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?

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

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?

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

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

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.

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

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 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.