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Title: The effects of different modes of selection in Drosophila melanogaster
Author: Shereif, N. A. K.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1987
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The components of stabilizing selection (fertility, mating speed, bilateral asymmetry) and effects of different patterns of selection in Drosophila melanogaster were studied using sternopleural, abdominal, ocellar, and orbital chaetae numbers. Fertility studies indicated reproductive superiority of intermediate sternopleural and orbital chaetae number phenotypes over extremes. Reproductive superiority was associated with higher heterozygosity with respect to allozyme loci. Studies of mating speed and fertility showed that both are correlated in a similar fashion with sternopleural chaetae number of male flies. A highly significant relationship between bilateral asymmetry of sternopleural chaetae number and heritability was found. Heritability values were higher when calculated for symmetrical than for asymmetrical parents. The effects of several different patterns of selection for sternopleural chaetae number were assessed. Conventional directional selection was compared with a pattern of directional selection incorporating an element of disruptive selection. Both resulted in similar directional responses to selection but the response with the disruptive pattern was attained with a lower selection differential resulting in a higher realized heritability. Decline in fertility was smaller in the disruptive selection lines. Differences between replicate selection lines were small and evidence suggests that a small number of genes lacking major viability effects account for most of the response to selection. The effect of conventional directional selection was compared in lines initiated from different regions of the base population distribution of sternopleural chaetae number. Differences in response were observed with lines initiated from the intermediate region showing the greatest combined response to divergent selection even though selection differentials were similar for all designs. The results are consistent with some dominance of factors increasing chaetae number, and with higher heterozygosity of intermediate phenotypes. It is concluded that the investigation of selection designs exploiting high heterozygosity may be of importance in the selective improvement of organisms useful to man.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available