Heterozygote Deficiencies and Allozyme-Associated Heterosis in Marine Bivalves

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Surveys of genetic variation in natural populations of marine organisms, particularly bivalves, have revealed a curious paradox: many genes show a deficiency of heterozygotes compared to frequencies expected under population genetic theory, yet at the same time heterozygous individuals appear to enjoy enhanced growth and survival. The reasons for this situation can only be understood by controlled laboratory experiments. In this project, over a hundred families of the coot clam, Mulinia lateralis, will be produced and reared in the laboratory. By comparing the genotypes of the parents and offspring in each family for a series of genes, the investigators will be able to determine the origin(s) of the numerical deficiency and enhanced fitness of heterozygote. One potential source is spontaneous chromosomal aberrations (aneuploidy) of the same type that cause a large proportion of birth defects in humans. If this proves to be the case, marine bivalves could become valuable model systems for the study of aneuploidy. Alternatively, if the fitness differences are attributable to biochemical differences in the gene products, this finding will further aid our understanding of the evolutionary significance of genetic variation in natural populations.