Sex Determination and Sex-Linked Characteristics

Chapter Four: Sex Determination and Sex-Linked Characteristics

COMPREHENSION QUESTIONS

1. What is the most defining difference between males and females?

Males produce relatively large gametes; females produce larger gametes.

*2. How do monoecious organisms differ from dioecious organisms?

Monoecious organisms exist as only one form, which has both male and female reproductive structures; the same organism produces both male and female gametes. Dioecious organisms exist as organisms of two distinct genders, one producing male gametes, the other producing female gametes.

3. Describe the XX-XO system of sex determination. In this system, which is the heterogametic sex and which is the homogametic sex?

In the XX-XO sex determination system, females have two copies of the sex-determining chromosome, whereas males have only one copy. Males must be considered heterogametic because they produce two different types of gametes with respect to the sex chromosome: either containing an X or not containing an X.

4. How does sex determination in the XX-XY system differ from sex determination in the ZZ-ZW system?

In the XX-XY system, males are heterogametic and produce gametes with either an X chromosome or a Y chromosome. In the ZZ-ZW system, females are heterogametic and produce gametes with either a Z or a W chromosome.

*5. What is the pseudoautosomal region? How does the inheritance of genes in this region differ from the inheritance of other Y-linked characteristics?

The pseudoautosomal region is a region of similarity between the X and Y chromosomes that is responsible for pairing the X and Y chromosomes during meiotic prophase I. Genes in this region are present in two copies in both males and females, and thus are inherited like autosomal genes, whereas other Y-linked genes are inherited only from father to son.

*6. How is sex determined in insects with haplodiploid sex determination?

Diploid individuals...