Question
Biology Question on Principles of Inheritance and Variation
Which of the following is correct ?
Henking discovered the small Y-chromosome
Drosophila also shows XX-XY sex determination like human
Birds have ZZ-ZW sex determination, where females are ZZ & males are ZW
Grasshoppers show XX-XY sex determination
Drosophila also shows XX-XY sex determination like human
Solution
Hermann Henking discovered the X chromosome while studying insects in the early 1890s. The sex chromosomes in birds are opposite of that in humans. Human males are heterogametic (XY), females are homogametic (XX), in birds males are homogametic (ZZ) and females are heterogametic (ZW). The "W" is the sex determining chromosome just as the Y in humans. A bird with a W is always a female. In grasshoppers, there is no Y chromosome, so a grasshopper with one X chromosome (symbolized as XO) is normally a male, while a grasshopper with two X chromosomes (XX) is normally a female.