Q38 - Haldane's Rule in Mosquitoes

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

J. B. S. Haldane (1892-1964), one of founders of the modern evolutionary biology, stated that if among hybrid offspring one sex is absent, rare, or sterile, that sex is the heterogametic one, i.e., in an X-Y sex-determination system, XY hybrids are preferentially sterile or inviable. Presgraves and Orr (1998) decided to test Haldane’s rule on taxa lacking a hemizygous X. They focused on the mosquitoes from the genera Aedes and Anopheles. In Aedes, males are XY and females are XX, but both X and Y chromosomes carry complete sets of homologous genes, while in Anopheles Y chromosomes are degenerate. They compiled the available data on the sterility of the hybrids resulted from crossing pairs of species in these taxa (tables below). Hint: Assume each character is controlled by many loci.

Using the information and data, determine which of the statements are true or which are false.

A. If the males in genus Anopheles were under strong selection, we would expect the same pattern of hybrid sterility as presented here.

B. The hybrid sterility patterns observed in both genera are consistent with the idea that alleles involved in hybrid sterility are recessive.

C. If the pattern of sterility in Aedes were identical to that of Anopheles, it would disprove Haldane's rule.

D. The pattern of hybrid sterility in Aedes suggest variation in Y chromosome functionality in this genus.

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Question reproduced from IBO 2018, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)