An insect species is discovered in which the heterogametic sex is unknown. An X-linked recessive mutation for reduced wing (rw) is discovered. Contrast the F₁ and F₂ generations from a cross between a female with reduced wings and a male with normal-sized wings when the female is the heterogametic sex.

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Accepted Answer

Hello everyone welcome back. Here's our next question. It says the sex in the blank is determined by a combination of many X. And Y chromosomes. So we can note right away, we're talking about many X and Y chromosome. So this is not similar to the human. That is not the same as in humans and other animals. Where you have either two exes or one X. And one Y. But many different ones. And that system is called choice D. The compound chromosome system. And in that compound chromosome system you can have several X chromosomes, several Y chromosomes or both of different, slightly different types and they function as a single sex determining group. So an example of this is in um roundworms or a certain kind of round work where females have pairs of autism's Plus eight pairs of x chromosomes While males, same number of autism's have eight x chromosomes Plus one Y chromosome. So you see that's different. You have this whole group multiple X chromosomes. So that's again the compound chromosome system. Let's look briefly at our other answer choices to understand why they are not correct. Um Choice a here and choice. See we have X chromosome, autism balance system and choice see the genic system. Um these kind of for the kind of two different names for the same thing. And that is that the primary determinant of sex is the ratio of X chromosomes to autism's. It is not dependent on the presence or absence of the Y chromosome. So again, this is both referring to the X chromosome autism balance system and the genic system sometimes called the genic balance system. So an example here is Drosophila, even though Drosophila does you see females having X. X. And males being X. Y. It is not the presence or absence of the Y. That determines a male phenotype. Rather its that ratio of X chromosomes to autism's. So when a female being 1 to 12 X chromosomes, two pairs of every autism in males, it's 1 to 21 X chromosome. For every two autism's that's the determiner of sex. So neither a nor C. Is referring to a combination of many X. And Y. So we're going to eliminate them. And then finally choice be the X. X. X. Y. System. Um This is present in humans and many other animals in which it is the presence or absence of the Y chromosome that determines sex phenotype in particular, the S. R. Y. Gene on the Y chromosome regardless of the number of exes. So uh in Turner syndrome, which is X. Zero. So just a single X chromosome, the phenotype is female because there is no Y chromosome with its S. R. Y. Gene, even though there's even though there's only a single X. Um versus inclined filter syndrome in which the individuals X. X. Y. Um And the phenotype is male because there is a Y chromosome. With its S. R. Y. Gene, even though there are two X chromosomes present. But again, we're not that's not talking about a combination of many X and Y. So not our answer here. So the sex in the choice T compound chromosome system is determined by a combination of many X and Y chromosomes. See you in the next video.

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Key Concepts

Heterogametic and Homogametic Sex Determination

X-linked Recessive Inheritance

Genetic Crosses and Generational Analysis (F1 and F2)