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Chapter 5: Problem 6

Describe the major difference between sex determination in Drosophila and in humans.

Short Answer

Expert verified
Answer: The major differences between sex determination mechanisms in Drosophila and humans are the mechanism itself and the key genes involved. In Drosophila, sex is determined by the X:A ratio, with the Sxl gene being the key regulator ensuring female development. In contrast, human sex determination depends on the presence or absence of the Y chromosome with an active SRY gene, which initiates male development.

Step by step solution

01

Introduction

In this exercise, we will explore the major differences between sex determination mechanisms in Drosophila and humans.
02

Understand Drosophila's Sex Determination System

In Drosophila, sex is determined by the ratio of X chromosomes to autosomes (non-sex chromosomes). The ratio is called the X:A ratio. Females have two X chromosomes and a ratio of 1, while males have one X and one Y chromosome and a ratio of 0.5. The higher X:A ratio in females leads to the upregulation of certain genes, mainly Sxl (Sex-lethal), which regulate sex-specific development and ensure female development.
03

Understand Human Sex Determination System

In humans, sex determination is governed by the presence or absence of the Y chromosome. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The key gene responsible for initiating male development is called SRY (sex-determining region on the Y chromosome). If a human embryo has a Y chromosome with an active SRY gene, it will develop male characteristics; otherwise, it will develop female characteristics.
04

Identify the Major Differences Between the Two Systems

After understanding the sex determination systems in Drosophila and humans, we can identify the major differences between them: 1. Mechanism: In Drosophila, the sex determination system is based on the X:A ratio, while in humans, it depends on the presence or absence of the Y chromosome with an active SRY gene. 2. Key genes: In Drosophila, the key gene controlling sex determination is Sxl, which is activated in females and leads to female development. In humans, the key gene is SRY, which is responsible for initiating male development.
05

Conclusion

The major difference between sex determination in Drosophila and humans lies in their mechanisms and the key genes involved. Drosophila uses the X:A ratio and the Sxl gene to determine sex, while humans rely on the presence or absence of a Y chromosome with an active SRY gene to determine sex.

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Most popular questions from this chapter

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?

Indicate the expected number of Barr bodies in interphase cells of individuals with (a) triple \(X\) syndrome \((X X X)\) (b) \(\mathrm{XYY}\) syndrome, (c) Klinefelter syndrome, (d) Turner syndrome, and karyotype \(48, \mathrm{XXXX}\)

When cows have twin calves of unlike sex (fraternal twins), the female twin is usually sterile and has masculinized reproductive organs. This calf is referred to as a freemartin. In cows, twins may share a common placenta and thus fetal circulation. Predict why a freemartin develops.

What specific observations (evidence) support the conclusions about sex determination in Drosophila and humans?

In chickens, a key gene involved in sex determination has recently been identified. Called \(D M R T 1\), it is located on the \(Z\) chromosome and is absent on the W chromosome. Like SRY in humans, it is male determining. Unlike \(S R Y\) in humans, however, female chickens (ZW) have a single copy while males (ZZ) have two copies of the gene. Nevertheless, it is transcribed only in the developing testis. Working in the laboratory of Andrew sinclair (a co- discoverer of the human \(S R Y\) gene), Craig Smith and colleagues were able to "knock down" expression of \(D M R T 1\) in \(Z Z\) embryos using RNA interference techniques (see Chapter 16 ). In such cases, the developing gonads look more like ovaries than testes [Nature 461: 267 (2009)]. What conclusions can you draw about the role that the DMRT1 gene plays in chickens in contrast to the role the SRY gene plays in humans?
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