Chapter 5: Problem 26

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?

Short Answer

Expert verified

Question: Compare the roles of DMRT1 gene in chickens and SRY gene in humans in terms of their involvement in sex determination and explain how they function distinctly based on gene dosage and chromosomal locations. Answer: Both DMRT1 in chickens and SRY in humans are involved in sex determination processes, but they function distinctly based on gene dosage and chromosomal locations. In chickens, having two copies of DMRT1 on the Z chromosome leads to male development, while having just one copy results in female development. In humans, the presence or absence of the SRY gene on the Y chromosome determines male or female sex, with no role for gene dosage.

Step by step solution

The DMRT1 gene is found in chickens and is responsible for sex determination, with male chickens having two copies (ZZ) and females having one copy (ZW) of the gene. DMRT1 is transcribed only in the developing chicken testis. However, when DMRT1 expression is knocked down in ZZ embryos, the gonads develop more like ovaries than testes. #Step 2: Understand the role of SRY in humans#

The SRY gene, found in humans, is also responsible for sex determination, but functions differently from DMRT1. In humans, the presence of the SRY gene on the Y chromosome determines male sex (XY), while its absence allows for the development of female sex (XX). #Step 3: Compare DMRT1 and SRY functions#

Comparing the two genes, both DMRT1 and SRY play a role in sex determination in their respective species. The major difference lies in the gene dosage and their location on sex chromosomes: DMRT1 is located on the Z chromosome of chickens and comes in one (female) or two (male) copies, while SRY is found on the Y chromosome in humans and is present only in males. #Step 4: Draw conclusions about the roles of DMRT1 and SRY in sex determination#

Based on the comparison of DMRT1 and SRY genes, we can conclude that both genes are involved in the sex determination process but function in distinct ways based on the gene dosage and chromosomal locations. In chickens, the presence of two copies of DMRT1 leads to the development of male-specific organs while having only one results in female-specific organs. On the other hand, in humans, the presence or absence of SRY is sufficient to determine male or female sex, with no role for gene dosage.