In mice, the Sry gene is located on the Y chromosome very close to one of the pseudoautosomal regions that pairs with the X chromosome during male meiosis. Given this information, propose a model to explain the generation of unusual males who have two X chromosomes (with an Sry-containing piece of the Y chromosome attached to one X chromosome).

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Hi everyone, welcome back, let's look at our next question. It says what is the most probable reason for being X. X. And fanatically male in a human? Well, first of all it's important to recall that in humans, the presence of a Y chromosome is the sex determining factor. So even if you have just a single X chromosome, you need the actual presence of the Y chromosome for that male phenotype. And that is specifically due to the S. R. Y. Gene found on that Y chromosome. And the S. R. Y. Gene is what's normal needed for male fanatic development. So we're looking for what is the most probable reason that an individual might be gina, typically X. X. But typically male. And that's going to involve needing somehow that S. R. Y. Gene to be present. So with that in mind, let's look at our answer choices choice. A says both the X chromosomes have homologous counterparts of the Y chromosome. Well, a Himalayas counterpart is not going to be sufficient. The S. R. Y. Gene is found only on the Y chromosome and you need that actual S. R. Y. Gene to be present somehow. So that's not an answer choice. B says one of the X chromosomes has an attached reason of the why that contains S. R. Y. Well, this would be our most probable region. We'd need the S. R. Y. Gene to be present. And so having an attached region of the Y. This could happen. There's a region of the X. And Y chromosome called the pseudo autism, A region that has enough similarity that you occasionally see a typical crossover between the two sex chromosomes. And if this occurs and that crossover region includes the S. R. Y. Gene. You could have a case. You now have an X chromosome containing the S. R. Y. Gene. Since that S. R. Y. Gene is sex determining. You could see a typical male development choice. He says one of the X chromosomes has mutations affecting female sexual development. Well, this is not our answer. Again, you have to have the S. R. Y. Gene as the sex determining factor. So mutation to your X chromosome is not going to cause a fanatical male development. And finally, choice. The both of the X chromosomes have an attached region of the Y chromosome, well having attached region in the Y chromosome, including that S. R. Y. Gene on both X chromosomes would cause a typical male development. Um however, having two copies of the S. R. Y. Gene might be an issue. And you don't, it says what is the most probable reason? Well, for both X chromosomes to have this atypical crossing over occur would not be more probable than choice be one of the X chromosomes having this so far more likely for that unusual cross over a typical crossover to occur in one X chromosome than in both. So that's why D is not correct. Since our answer choice. Our questions specifically asked for the most probable reason. So again, that most probable reason for being XX and typically male and a human is choice. Be one of the X chromosomes has an attached region of the Y that contains S. R. Y. Thanks for watching. See you in the next video.

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Key Concepts

Pseudoautosomal Regions and Chromosome Pairing

Sry Gene and Sex Determination

Chromosomal Translocation and Unusual Karyotypes