Article Abstract:
A novel test is used in assessing whether lethal hybrid mutations affect both sexes in Drosophila melanogaster. Mutations at the transformer (tra) locus of the Drosophila sex determination pathway are used in transforming the somatic sex of D. melanogaster-D. simulans hybrids. The tra is the first gene in the sex determination cascade that affects sex determination alone. Results indicate that the lethality of the hybrids is dependent on the hybrid sex chromosome genotype and not on somatic sex. The primary hybrid incompatibility depends on sex chromosome genotype while the hs-tra show that sex determination mechanisms do not diverge at fast rates.
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Article Abstract:
Theoretical and empirical difficulties in the theory that the loss of fitness among unisexual hybrids implied by large X chromosomal defects and the Haldane's ruleis the result of meiotic drive are discussed. In contrast to this theory, the large effect of the X chromosome and Haldane's rule can be explained by the higher frequency of underdominant or partially recessive favorable allele substitution in the X chromosome compared with the autosomes.
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Article Abstract:
A previous analysis of Haldane's rule has been criticized for proposing a simple dominance theory to explain the rule. However, the critics fail to take into account that any explanation of Haldane's rule would naturally focus on the rule itself, rather than on the exceptions. Moreover, the analysis does not claim that all hybrid incompatibilities act as recessives, as the critics say they do.
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