Lack of degeneration of loci on the neo-Y chromosome of Drosophila americana americana.
The extent of genetic degeneration of the neo-Y chromosome of Drosophila americana americana has been investigated. Three loci, coding for the enzymes enolase, phosphoglycerate kinase and alcohol dehydrogenase, have been localized to chromosome 4 of D. a. americana, which forms the neo-Y and neo-X chromosomes. Crosses between D.a. americana and D. virilis or D. montana showed that the loci coding for these enzymes carry active alleles on the neo-Y chromosome in all wild-derived strains of americana that were tested. Intercrosses between a genetically marked stock of virilis and strains of americana were carried out, creating F3 males that were homozygous for sections of the neo-Y chromosome. The sex ratios in the F3 generation of the intercrosses showed that no lethal alleles have accumulated on any of the neo-Y chromosomes tested. There was evidence for more minor reductions in fitness, but this seems to be mainly caused by deleterious alleles that are specific to each strain. A similar picture was provided by examination of the segregation ratios of two marker genes among the F3 progeny. Overall, the data suggest that the neo-Y chromosome has undergone very little degeneration, certainly not to the extent of having lost the functions of vital genes. This is consistent with the recent origin of the neo-Y and neo-X chromosomes, and the slow rates at which the forces that cause Y chromosome degeneration are likely to work.
Charlesworth
B
B
Department of Ecology and Evolution, University of Chicago, IL 60637-1573, USA. bcworth@pondside.uchicago.edu
Charlesworth
D
D
Hnilicka
J
J
Yu
A
A
Guttman
D S
DS
D000818:Animals; D004303:Dosage Compensation, Genetic; D004330:Drosophila / Q000235:genetics*; D004798:Enzymes / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D005804:Genes, Lethal; D008040:Genetic Linkage; D005819:Genetic Markers; D006824:Hybridization, Genetic; D019476:Insect Proteins / Q000235:genetics; D008297:Male; D009154:Mutation; D012744:Sex Ratio; D013045:Species Specificity; D014960:X Chromosome / Q000235:genetics; D014998:Y Chromosome / Q000235:genetics*
D004798:Enzymes; D005819:Genetic Markers; D019476:Insect Proteins