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D J Merrell

Publications and source records attributed to D J Merrell.

7 recordsLinked to original sources
PubMed1977

Chromosomal analysis of DDT-resistance in a long-term selected population of Drosophila melanogaster.

The genetic basis of DDT-resistance was studied in a population of Drosophila melanogaster. This population was unique in that it had been continually selected for DDT-resistance since 1952 and had achieved a very high level of resistance. The genetic basis of resistance was studied by means of a chromosomal analysis. Fifteen combinations of resistant and control chromosomes were tested using a time-based DDT test. The analysis of the data showed that resistance was multifactorial with each of the three major chromosomes involved. Dominant and recessive second and third chromosome effects were found to be much more important than those of the first chromosome, which had no detectable recessive effects. Second and third chromosome resistance genes showed incomplete dominance. The average dominance of the second chromosome was much less than that of the third chromosome. These large-scale differences between chromosomes' effects and average dominance may indicate that a small number of resistance genes are involved. Two significant interactions between chromosomes were found. Scaling difficulties make the interactions difficult to interpret without further data. It seems possible that positive interactions between resistance have been developed by the long-term directional selection in this population.

Animals↗
PubMed1972

Laboratory studies bearing on pigment pattern polymorphisms in wild populations of Rana pipiens.

Data are presented for 2,393 progeny from a number of crosses related to a study in ecological genetics of the Burnsi and Kandiyohi polymorphisms in natural populations of the leopard frog, Rana pipiens. No significant differences in viability were found between wild-type homozygotes (+/+) and Burnsi heterozygotes (B/+) or homozygotes (B/B). Similarly, no difference in viability was found between wild-type (+/+) and Kandiyohi heterozygotes (K/+) and homozygotes (K/K). However, there appears to be slight reduction in viability of the double dominant heterozygote (B/+; K/+) in comparison with (+/+), (B/+), and (K/+) progeny from the same cross.-The Kandiyohi heterozygotes (K/+) appeared to have a more rapid rate of development from fertilization through metamorphosis than wild-type (+/+) or Burnsi (B+/) or Burnsi-Kandiyohi heterozygotes (B+K/+). Since Kandiyohi is associated primarily with the prairie habitat (Merrell 1965), this finding suggests that the adaptive advantage of Kandiyohi lies in the more rapid rate of development of frogs carrying this gene, enabling them to complete metamorphosis before the prairie breeding ponds dry up.-Data are presented from crosses involving dorsal spot number. The results suggest that heredity plays a role in the determination of dorsal spot number but that non-genetic influences are also of considerable importance.-The results of these crosses are discussed with respect to their bearing on the formation of pigment patterns in Rana pipiens. From the available data it is clear that the pigment pattern in Rana pipiens is a complex trait influenced by major gene loci, by modifying genes, and by environmental effects. The relative importance of these factors varies depending on the particular combination of genetic and environmental conditions.

Adaptation, Biological↗