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Gene Frequencies in Mass-Selected Corn Populatios and in Derived Random Inbred Lines¹

The use of randomly developed lines from a population for estimating genetic variances requires the assumption that gene frequencies are unaffected by natural selection and remain constant with inbreeding. To determine whether gene frequencies were in fact influenced by natural selection, starch gel electrophoresis was used to identify genotypes at 10 isozyme loci in three corn (Zea mays L.) populations and in random lines derived from them. Two of the populations had been improved by 15 cycles of mass selection for increased grain yield. One of these improved populations had received thermal neutron treatments at Cycle 0 and after one cycle of selection. The other population studied was the original open-pollinated cultivar. Allelic freqencies in random lines derived from massselected populations were affected little by inbreeding. However, natural selection appeared to have more impact on allelic frequencies of lines developed from the original cultivar, suggesting that deleterious recessive alleles were reduced in frequency by mass selection. Changes in allelic frequencies associated with mass selection were noted for Estl and Prx1 in the irradiated and control populations. Gametic phase disequilibrium was not widely detected in the inbred lines, but was common for loci in combination with Mdh2.

Key Words: Isozymes • Electrophoresis • Genetic variance • Zea mays L. • Mutation breeding

² Former graduate research assistant (presently, Dep. of Genetics, North Carolina State Univ.), Foundation professor, and adjunct assistant professor, respectively, Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583-0915.

Received for publication March 24, 1986.