Abstract
It has been stated that in new gene pools, several generations of random mating should precede artificial selection. The effects of such an approach were studied in four maize (Zea mays L.) gene pools which differed in degree of diversity, adaptation, and number of previous cycles of recombination. The gene pools were developed for several generations under open pollination and high plant densities. Seed was bulked from standing plants which were bordered, disease-free, and produced a well-filled, normally developed ear; this included 0.5–3% of the total plant stand. Various generations of each gene pool were compared to determine any changes in plant characteristics and extent of genetic variability. The major phenotypic changes occurred during the first one or two generations of random mating and were those that allowed the population to make maximum use of the available growing season: the earliest maturing population became later and larger in stature; conversely, the least adapted population became earlier and smaller in stature. The general tendency in all gene pools was a decrease in estimates of genetic variability from early to later generations. Estimates of genetic variability tended to be highest in populations containing exotic materials.
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