SEX-CHROMOSOME EVOLUTION AND HALDANES RULE

Haldane observed that where interspecies hybrids show sex differences in sex ratio or fertility, it is always heterogametic sex which is aff ected, Many hypotheses have been advanced to explain Haldane's rule, b ut it is difficult to find a unifying explanation that will accommodat e male and female heterogamety, and explains why fertility, especially , is affected, Here we propose that asymmetry can be accounted for by interactions involved in determining male dimorphisms or fertility bet ween genes which diverged from allele pairs on the X and Y. Failure of one or more heterospecific interactions will render the male sterile. Similar arguments may be made for other groups with male or female he terogamety, and the argument can be extended to account for Y-(or W-) autosome interactions.