EVIDENCE OF EVOLUTIONARY FORCES LEADING TO THE SPREAD OF LETHAL GENES IN WILD POPULATIONS OF HOUSE MICE

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Abstract
An evolutionary force, additional to those usually considered effective in altering gene frequencies (mutation, selection, random genetic drift and migration), is found to play the dominant role in determining the frequency of lethal alleles at locus T in populations of wild house mice. The new force, male segregation ratio, changes the normal ratio from 0.5 to an average of 0.96 in favor of the mutant allele. Thirteen alleles from 12 different wild populations from different parts of the United States all show similar segregation ratios. This advantage favors the maintenance and spread of lethal alleles. In addition, preliminary evidence indicates that animals heterozygous for such alleles have a selective advantage over those of normal genotype during early reproductive life. The effects of these facts on equilibrium values of such alleles in wild populations are discussed.