3. Extensions to Mendelian Inheritance

Sex Chromosome

Open Question
Cat breeders are aware that kittens expressing the X-linked calico coat pattern and tortoiseshell pattern are almost invariably females. Why are they certain of this?
Multiple Choice
Which of the follow sex chromosomes can be describes as homogametic?
Multiple Choice
In the ZZ/ZW sex determination system, the male is…?
Multiple Choice
In humans, which region on the Y chromosome determines maleness?
Multiple Choice
During meiosis the XY sex chromosomes segregate independently. Which of the following represents the gametes chromosomes after meiosis?
Open Question
How do we know that X chromosomal inactivation of either the paternal or maternal homolog is a random event during early development in mammalian females?
Open Question
How do we know that Drosophila utilizes a different sex-determination mechanism than mammals, even though it has the same sex-chromosome compositions in males and females?
Open Question
In this chapter, we have focused on sex differentiation, sex chromosomes, and genetic mechanisms involved in sex determination. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, you should answer the following fundamental questions?How do we know that in humans the X chromosomes play no role in human sex determination, while the Y chromosome causes maleness and its absence causes femaleness?
Open Question
In this chapter, we have focused on sex differentiation, sex chromosomes, and genetic mechanisms involved in sex determination. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, you should answer the following fundamental questions?

How do we know whether or not a heteromorphic chromosome such as the Y chromosome plays a crucial role in the determination of sex?
Open Question
Write a short essay that discusses sex chromosomes as they contrast with autosomes.
Open Question
Distinguish between the concepts of sexual differentiation and sex determination.
Open Question
Contrast the XX/XY and XX/X0 modes of sex determination.
Open Question
Describe the major difference between sex determination in Drosophila and in humans.
Open Question
How do mammals, including humans, solve the 'dosage problem' caused by the presence of an X and Y chromosome in one sex and two X chromosomes in the other sex?
Open Question
The phenotype of an early-stage human embryo is considered sexually indifferent. Explain why this is so even though the embryo's genotypic sex is already fixed.