Introduction of a Lethal Allele into a Feral House Mouse Population

Abstract

House mice heterozygous for the recessive lethal allele twl1 were released in 1956 and in 1957 on Great Gull Island, Long Island Sound, New York. The feral population of this island was believed to be free of such alleles on the basis of samples taken and tested previously. Heterozygotes were found among mice captured on the island in 1959, 1960, 1961, and 1962, and cross-testing indicates that the allele now present is that which was introduced. Systematic sampling over the whole island indicates that by 1961 the allele had reached high frequency in the 1957 release area, but was spreading very slowly. It appears, therefore, that introduction of the lethal was successful despite the operation of selection against the homozygotes. This is attributed to the male transmission ratio advantage and is in accord with some of the predictions of theoretical models.