In a number of organisms, including Drosophila and butterflies, genes that alter the sex ratio have been described. In the pest species Musca domesticus (the house fly), Aedes aegypti (the mosquito that is the vector for yellow fever), and Culex pipiens (the mosquito vector for filariasis and some viral diseases), scientists are especially interested in such genes. Sex in Culex is determined by a single gene pair, Mm being male and mm being female. Males homozygous for the recessive gene dd never produce many female offspring. The dd combination in males causes fragmentation of the m-bearing dyad during the first meiotic division, hence its failure to complete spermatogenesis.
(a) Account for this sex-ratio distortion by drawing labeled chromosome arrangements in primary and secondary spermatocytes for each of the following genotypes: Mm Dd and Mm dd. How do meiotic products differ between Dd and dd genotypes? Note that the diploid chromosome number is 6 in Culex pipiens and both D and M loci are linked on the same chromosome.
(b) How might a sex-ratio distorter such as dd be used to control pest population numbers?
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