We have investigated the effect of sex chromosome constitution on preimplantation development in embryo progeny from homogametic and heterogametic females.
Table 1 Differential preimplantation developmental rate in embryo progeny from heterogametic ([XY.sub.*]) and homogametic (XX) females of Akodon azarae.
The same Spiroplasma kills males in ladybirds (male heterogametic) and butterflies (male
homogametic).
Their importance is also suggested by theoretical work on Haldane's rule, which states that the viability or fertility of the heterogametic sex is more likely than that of the
homogametic sex to be reduced in hybrids (Haldane 1922).
This may be due to the sex in papaya which is determined by a single gene with three alleles, in which males and hermaphrodites are heterogametic, while females are
homogametic [24, 25].
Normally, the heterogametic sex (males in XY/XX systems, females in ZW/ZZ systems) shows lower chiasma frequencies than the
homogametic one (Trivers 1988, Burt et al.
When both loci are autosomal, or when all sampled individuals are of the
homogametic sex, then this method reduces to the form given in Hill (1974).
Although Haldane's rule applies to asymmetrical sterility or viability between
homogametic and heterogametic hybrids in most diploid species, it is not directly relevant to species with other sex determination systems simply because they lack sex chromosomes and a heterogametic sex.
Haldane (1922) observed that when hybridization occurs between different animal races, the heterogametic sex more often suffers reduced survivorship or fertility than the
homogametic sex.
vanbrunti produced rates of fertilization almost equal to those involving
homogametic crosses, and that sperm of E.