Selection or Drift–Isozyme Allele Frequency Changes among Channel Catfish Selected for Rapid Growth

Publisher Website
Google Scholar
Abstract
Enzyme allele frequencies at 28 loci were determined within nine lines of channel catfish Ictalurus punctatus selected for rapid growth and within their respective control lines. Thirteen of the 28 loci were polymorphic. There were differences among lines for frequencies of alternative alleles and for heterozygosity. Related lines had similar biochemical genetic character, but significant differences in allele frequencies were noted between control and select lines in as little as one generation. Lines derived by crossbreeding followed by selection had the least genetic variability. In general, selected lines had lower mean heterozygosity, lower percentages of polymorphic loci, and fewer alleles per locus than control lines. Heterogeneity of Wrightˈs fixation indices, and the observed magnitude of change for allele frequencies compared to that expected from genetic drift, indicated selection for rapid growth caused the differences in enzyme allele frequencies between select and control lines at some loci. Actual measurement of drift by observing allele frequency changes between generations indicated selection within 9 of 13 polymorphic loci for at least one line of channel catfish per locus. Possession of certain allozymes partially explains growth differences between selected channel catfish and their randomly bred controls; such allozymes may have direct physiological effects on growth or their alleles may be linked to others affecting rate of growth.