Decrease In Genetic Diversity Research Articles

Rate of Decrease of Genetic Variability in a Subdivided Population

Rate of Decrease of Genetic Variability in a Subdivided Population

Genetic Variances in Populations Developed from Full‐Sib and S 1 Testcross Progeny Selection in an Open‐Pollinated Variety of Maize 1

A nested Design I consisting of full-sib and half-sib families was used to study changes in genetic variances resulting from two selection systems in the ‘Krug’ yellow dent variety of maize (Zea mays L.). Two populations derived from Krug on the basis of earlier Design I experiments were used. K (S1) syn-2 was developed by intercrossing S1 progenies of the male parent of selected half-sib families. The second population, K (FS) syn-2 was developed by intercrossing remnant seed of selected full-sib progenies. Both selected populations, K (FS) syn-2 and K (S1) syn-2, were significantly higher yielding than the original variety, Krug. Design I matings were made within each of the two selected populations to provide evidence on changes in genetic variances that had occurred from the selection practiced. Selection resulted in a moderate decrease in genetic variance, with S1 progeny and full-sib selection producing, apparently, different changes in magnitude of genetic variances

A Developmental Study of Recessive Lethals from Wild Populations of Drosophila melanogaster

Samples of Drosophila melanogaster from three populations of common origin were examined for their load of recessive lethals. Two of the samples were collected from wild populations in Berea, Kentucky, on successive years and a third sample was obtained from a laboratory population, initiated with flies from a wild population and maintained for an eight month period. These samples were tested for frequency of second chromosome recessive lethals, for allelism rate and for ontogenetic distribution of lethality of the lethal factors. The frequency of recessive lethals in the samples from wild populations in 1959 and 1960 were 31.4 per cent and 37.4 per cent, respectively, and that of the laboratory population was 23.4 per cent. The allelism rates for the lethal factors in the three populations were 0.9 per cent, 2.4 per cent and 3.1 per cent, respectively. The ontogenetic distributions of lethal action of the mutants in the three Berea samples, in an earlier sample from a Wisconsin wild population, and in a group of spontaneous lethals were not significantly different, each with a large majority (56 to 72 per cent) which were effective in the larval stage. This suggests strongly that the effects (or lack of effect) of natural selection are the same in all of these ontogenetically different types of lethals. It appears that the genetic variability, as measured by the recessive lethal frequency, allelism rate and ontogenetic distribution of lethality of the lethals, is about the same from year to year in the areas studied. When a sample of wild population was transposed into population cages, there appeared to be an overall decrease in genetic variability.