Translocation heterozygosity, genetic heterozygosity, and inbreeding in Clarkia speciosa

The abundance of floating translocation heterozygotes in natural populations of many species has been explained most commonly as due to a superiority of the translocation heterozygote-particularly under conditions of inbreeding. Theoretically this is an attractive explanation but very little direct evidence has been produced to substantiate it. Evidence on this hypothesis was obtained from the forced inbreeding of naturally occurring translocation heterozygotes and comparison of sibling translocation heterozygotes and homozygotes within the inbred progeny. The data obtained provide strong evidence that translocation heterozygosity is correlated with genetic heterozygosity in inbred progenies of Clarkia speciosa. Three of four different translocation heterozygotes when self pollinated produced progenies in which translocation heterozygotes were clearly larger (mean and maximum values) and less variable than homozygotes. In all of the four progenies tested the translocation heterozygotes were characterized by much lower frequencies of unpaired chromosomes relative to sibling homozygotes. The maintenance of translocation heterozygosity in Clarkia speciosa is undoubtedly maintained, at least in part, by the higher average level of genetic heterozygosity of translocation heterozygotes under conditions of severe inbreeding such as often found in natural populations.