In chickens, a key gene involved in sex determination has recently been identified. Called DMRT1, it is located on the Z chromosome and is absent on the W chromosome. Like SRY in humans, it is male determining. Unlike SRY 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 SRY gene), Craig Smith and colleagues were able to 'knock down' expression of DMRT1 in ZZ embryos using RNA interference techniques (see Chapter 18). 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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Hi everyone, Let's look at our next question. It says which of the following organisms has homo comedic males? And hetero comedic females lets just recall briefly those terms homo comedic and hetero comedic. Um of course, home a comedic means um having only one type of sex chromosome, meaning of course that all of their gametes will be the same. Since there's only the one type of sex chromosome. And hetero comedic of course, meaning more than one type. So there's several different systems, of course, of sex determination. Um There's the X. X. X. Zero system and this would be found mainly in insects. And this is where sex is determined by how many of the sex chromosomes are present. So if there's two X. Is the sex is female and if there's only one, the sexes male. So it's not determined by the presence of a Y chromosome. For instance, even if there is like in fruit flies, the males do have a Y chromosome, but sex is determined by how many exes are present. Then there's um what we know from humans, the X. X. X. Y. System. And that's where sex is determined by the presence of this Y chromosome. And in keeping with our question here, um we know that females our home a comedic and males are hetero comedic with that um Y chromosome being the sex determiner carries that S. R. Y. Gene that determines male development, then there's a third system which is called the ZZ ZW system. And this is just the opposite of X. X. X. Y. So in this system the females are actually, let's do it in the other order since I said it's easy first, the males are homo comedic. So males are Zz they have two of the same sex chromosome and the females our hetero comedic. So females are determined by the Z. W. Um genotype and in this case that w gene does carry genes that determine female sexual development. And this system is common in birds um amphibians and reptiles. So it works the same way in terms of inheritance. You draw the same kind of put it square, it's just reversed as to which sex is home. A comedic in which hetero comedic. So with that in mind let's look through our answer choices. Um choice a says humans. And of course as we saw humans are the opposite with hetero comedic males and females since their that X. X. X. Y. System, insects. We said it determined their sex is determined by how many of the X chromosome they have. So that is not the case here. And then Choice C. Is birds and birds is our correct answer because sex determination in birds is determined by that Zzz W system where the males are zz the males are home a comedic and the females are ZW hetero comedic. So exactly the reverse of what we find in humans. And then finally, choice. Deep mice, mice is not an answer because mice um like most placental mammals are the same as humans. They follow the XX XY system so the reverse of what our questions asking for. So again, which of the following organisms has home a dramatic males and hetero comedic females. Choice sea birds. See you in the next video.

Verified Solution

Key Concepts

Sex Determination Genes

Chromosomal Differences in Sex Determination

RNA Interference Techniques