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Chapter 5: Problem 3

As related to sex determination, what is meant by (a) homomorphic and heteromorphic chromosomes; and (b) homogametic sex and heterogametic sex?

Short Answer

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Question: Define and differentiate between the following terms related to sex determination: (a) Homomorphic chromosomes and Heteromorphic chromosomes, (b) Homogametic sex and Heterogametic sex. Answer: (a) Homomorphic chromosomes are identical sex chromosomes in size, shape, and gene content, whereas heteromorphic chromosomes differ in these aspects. Homomorphic chromosomes are found in individuals from the same sex, while heteromorphic chromosomes are distinctly different between the two sexes, such as the human XY sex determination system. (b) Homogametic sex refers to the sex that produces gametes with identical sex chromosomes (e.g., human females with XX chromosomes). In contrast, heterogametic sex refers to the sex that produces gametes with different sex chromosomes (e.g., human males with XY chromosomes).

Step by step solution

01

Homomorphic chromosomes

Homomorphic chromosomes are chromosomes that are the same size and shape and have the same genes in the same locations. In the context of sex determination, they would refer to the sex chromosomes that appear identical in a particular sex.
02

Heteromorphic chromosomes

Heteromorphic chromosomes are chromosomes that differ in size, shape, or gene content. In terms of sex determination, they refer to the sex chromosomes that are distinctly different between the two sexes. An example of this is the human XY sex determination system, where the X and Y chromosomes are heteromorphic.
03

Homogametic sex

Homogametic sex refers to the sex that produces gametes with identical sex chromosomes. In other words, the sex that has two homomorphic sex chromosomes. For example, in humans and many other species, the female is the homogametic sex, as they possess two X chromosomes (XX).
04

Heterogametic sex

Heterogametic sex refers to the sex that produces gametes with different sex chromosomes (heteromorphic chromosomes). This means that the individuals of this sex carry two different sex chromosomes. For example, in humans and many other species, the male is the heterogametic sex, as they possess one X and one Y chromosome (XY).

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Most popular questions from this chapter

Review the Chapter Concepts list on p. \(83 .\) These all center on sex determination or the expression of genes encoded on sex chromosomes. Write a short essay that discusses sex chromosomes as they contrast with autosomes.

In mice, the X-linked dominant mutation Testicular feminization (Tfm) eliminates the normal response to the testicular hormone testosterone during sexual differentiation. An XY mouse bearing the \(T f m\) allele on the \(X\) chromosome develops testes, but no further male differentiation occurs-the external genitalia of such an animal are female. From this information, what might you conclude about the role of the Tfm gene product and the X and \(Y\) chromosomes in sex determination and sexual differentiation in mammals? Can you devise an experiment, assuming you can "genetically engineer" the chromosomes of mice, to test and confirm your explanation?

It is believed that any male-determining genes contained on the Y chromosome in humans are not located in the limited region that synapses with the X chromosome during meiosis. What might be the outcome if such genes were located in this region?

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: (a) How do we know that in humans the X chromosomes play no role in sex determination, while the Y chromosome causes maleness and its absence causes femaleness? (b) How did we originally (in the late 1940 s) analyze the sex ratio at conception in humans, and how has our approach to studying this issue changed in \(2015 ?\) (c) 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? (d) How do we know that Drosophila utilizes a different sexdetermination mechanism than mammals, even though it has the same sex-chromosome compositions in males and females?

Describe how nondisjunction in human female gametes can give rise to Klinefelter and Turner syndrome offspring following fertilization by a normal male gamete.
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