Female Heterogamety in Birds — NEET Biology
📚 Practice ConceptIn the above description you have studied about two types of sex determining mechanisms, i.e., XO type and XY type. But in both cases males produce two different types of gametes, (a) either with or without X-chromosome or (b) some gametes with X-chromosome and some with Y-chromosome. Such types of sex determination mechanism is designated to be the example of male heterogamety. In some other organisms, e.g., birds, a different mechanism of sex determination is observed. In this case the total number of chromosome is same in both males and females. But two different types of gametes in terms of the sex
Which of the following statements accurately describe aspects of gamete formation and sex determination? S1: In the XY sex determination system, males are heterogametic because they produce two types of gametes, one carrying X and the other carrying Y. S2: Females in the ZW sex determination system are homogametic, producing only one type of gamete (Z). S3: Organisms with XO sex determination exhibit male heterogamety, as males produce gametes with and without the X chromosome. S4: In all cases of male heterogamety, the male necessarily possesses a Y chromosome along with an X chromosome. S5: A zygote formed by the fusion of an X-carrying sperm and an X-carrying ovum in humans will develop into a male offspring.
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Correct answer: A — S1 and S3 are correct.
S1 is correct. In the XY system (e.g., humans, Drosophila), males are XY and thus heterogametic, producing two types of sperm (X-carrying and Y-carrying). S2 is not correct. In the ZW system (e.g., birds), females are ZW and thus heterogametic, producing two types of eggs (Z-carrying and W-carrying). Males (ZZ) are homogametic. S3 is correct. In the XO system (e.g., grasshoppers), males are XO and are heterogametic, producing two types of sperm (X-carrying and gametes lacking X). S4 is not correct. Male heterogamety includes both XY (where males have X and Y) and XO (where males have X but no Y) systems. S5 is not correct. In humans, the fusion of an X-carrying sperm and an X-carrying ovum results in an XX zygote, which develops into a female offspring. Therefore, statements S1 and S3 are correct.
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