Inheritance of a chromosomal polymorphism in odd-year pink salmon from southeastern Alaska

Abstract

In previous work we found a high frequency of heterozygotes for a fission translocation involving the seventh chromosome pair in odd-year populations of pink salmon (Oncorhynchus gorbuscha) sampled from Washington State to south central Alaska. The populations from southeastern Alaska and northern British Columbia had high frequencies of heterozygotes for a second rearrangement of this same chromosome pair. In these fish one fission product, the larger acrocentric chromosome bearing the nucleolar organizer region (NOR), has undergone an inversion to produce a submetacentric chromosome. In this paper, we present inheritance data on pink salmon from the Gastineau hatchery stock in Juneau, Alaska, where individuals with the two rearrangements are found. Although most of the fish were either homozygous for the normal cytotype or heterozygous for the inversion cytotype, a few individuals heterozygous for the fission cytotype were found. Ten males and ten females were karyotyped, and crosses were set up in all combinations. Individuals with both rearrangements were found in crosses between the two types of heterozygotes, and the ratios of cytotypes in the progeny did not deviate significantly from the expected values. No significant difference in viability of offspring from crosses between individuals with different cytotypes was found up to the age of hatching.Key words: salmon, chromosomal polymorphism, translocation, inversion, cytotype.