A Comparative Study of the Esterase - 5 Locus 1 N Drosophila Pseudoobscura

Electrophoretic phenotypes of the esterase5 locus were examined in the sibling species D. pseudoobscura, D. persimilis and D. miranda. D. persimilir alleles were found to have uniformly higher charge on monomers than corresponding alleles of either D. pseudoobscura or D. miranda. Consequently. D. persimilis shares no alleles in common with either D. pseudoobscura or D. miranda, while the latter two species share a number of alleles. It was discovered that hy increasing the concentration of acrylamide gel and increasing the length of migration, more allelic differences could be distinguished. Also mare alleles were discovered by examining monomer mobility in addition to dimer mobility. In D. persimilis and D. miranda it was found that the previously known high frequency allelic classes broke down into several allelic classes. A test of goodness-oi-fit to the infinite alleles model was done and a rough agreement with the model was found. AN important quantity in molecular population genetics is the number of allelic forms of genetic loci coding for proteins in natural populations. The most common method used to detect genetic polymorphism of enzyme loci is gel electrophoresis. I t has been proposed that routine methods of gel electrophoresis allow the investigator to detect roughly 27% of new mutations involving a change of a single amino acid (LEWONTIN 1974). Consequently, it is suspected that there are more alleles present in samples than have been reported in past studies. In addition to the question of how many alleles are present in populations, there is much interest in the number and frequency of alleles common to related species. I t is possible that some electromorphic alleles which are common torelated species are not the same but rather have differences that are not revealed by routine methods of electrophoresis. This latter possibility is of particular interest, as the observation of the same electromorphic alleles in related species has been used in arguments attempting to distinguish between alternative models explaining the existence Olf enzyme polymorphisms (LEWONTIN 1974). The esterase-5 locus in the sibling species Drosophila pseudoobscura, D. persimilis and D. miranda is of interest, as it has been found to be highly polymorphic Genetics 85: 697-711 Apnl, 1977. 698 C. COBBS A N D S. PRAKASH in all three species.There are 15 alleles known in D. pseudoobscura (PRAKASH, LEWONTIN and HUBBY 1969; COBBS 1976), 6 alleles in D. prrsimilis (PRARASH 1969) and 5 alleles in D. miranda (PRAKASH, 1977). The Est-5’.07 and E ~ t 5 ’ . ’ ~ mobilities exist in all three species (PRAKASH, 1977 and present data). This paper will report that with relatively minor changes in the methods of electrophoresis we have been able to find many more alleles in both D. persimih and D. miranda. We have found that D. persimilis has no allele in common with either D. pseudoobscura or D. miranda. D. pseudoobscura and D. miranda have some alleles which, so far: appear to be common to both species. MATERIALS A N D METHODS Coll~ctions: Forty-thrre isofemale lines of D. prrsirnilis collected from Mother, California in 1968 were sib mated until electrophoretically homozygous lines were obtained. These lines had been kept in vials for a numhrr of years h h r e Fib matings and very fcw of them were sepregating for electrophoretic alleles. Thirty-thrce isofeniale lines of D. mirunda collcctcd from Sisters. Oregon in 1969 were also treated in thr above manncr. Again very frw of thrse lines were segrrgating for electrophoretic alleles. Thirty D. pseudoobscuru lines were derived as ahove from a sample taken at Mesa Verde, Colorado in 1971. Electrophoresis: Vertical acrylamide gel electrophoresis was performed according to the methods of Hunw and LEWONTIN (1966). The steps of ccntrifugifig and iinmersion of the gel in boric acid solution for the staining of esterase-5 were omitted. The concentration of acrylamide varied from 4% to 12% and the grls were run for longer periods of time. The time of electroEst-5 monomer dimer Est-5