Fitness of Heterozygotes in Barley1

Abstract

The level of dominance at four loci for reproductive fitness was investigated in barley (Hordeum vulgare L,.). Each of the four loci contained a recessive allele, believed to be of spontaneous origin, that is a seedling chlorophyll lethal when homozygous. Populations were established with initial gene frequency of p = .5, and the proportion of normal green to defective seedlings was ascertained in successive selfed generations. Reproductive fitness of the normal homozygote vs the normal heterozygote was indicated in the rate of elimination of the defective allele.The rate of elimination of the defective allele in ‘Colsess I,’ Colsess II,' ‘Xantha 3,’ and ‘Albino 7’ indicated approximately equal fitness of the normal homozygote and heterozygote, thus suggesting a complete dominance interpretation for reproductive fitness. Small deviations from the dominance model in the direction of partial dominance or over‐dominance were about equally frequent for the Colsess I, Xantha 3, and Albino 7 loci. The allele in Colsess II, decreased in frequency at a rate slightly slower than predicted by the dominance model; however, if over‐dominance was present, it was modest. These data, which support a dominance explanation for reproductive fitness, are in conflict with findings on chlorophyll lethals in corn (Zea mays L.) and with reports on heterozygote advantage for agricultural fitness at the Xantha 3 and Albino 7 loci.