Genetics of Natural Populations of Drosophila nasuta

Abstract

Chromosomal polymorphisms in Drosophila nasuta populations from the north and northeastern parts of India were studied. A total of 22 heterozygous inversions were detected. Among them, 16 were previously undescribed gene arrangements. The X chromosome has one inversion, the 2L chromosome arm has two, the 2R chromosome arm has four, and chromosome 3 has 15 inversions. Three heterozygous inversions, 2L-2, 3-2, and 3-35, were very common and detected in high frequencies In all populations examined. Several rare inversions were detected only once. Further, the mean number of heterozygous inversions per individual varies from 1.70 to 2.76. The highest frequency of heterokaryotypes Is on chromosome 2L, and the lowest Is on the X chromosome.

Allele frequency estimates when only heterozygotes can be recognized: method of estimation and application in the case of chromosomal inversion polymorphisms in Drosophila

“…We calculated the correlation between inversion frequencies (after angular transformation) and altitude: it is significant and positive for inversion A (r = 0945; 3 df; P < 002) and P>oos. (Clyde, 1982;Kumar and Gupta, 1988;Mather and Thongmeearkom, 1980). Unfortunately, however, most authors have published only the heterozygosity for each inversion and not the frequencies of the various heterozygotes-which are the critical data for analysis.…”

“…nebulosa: Da Cunha ci a!., 1953; for D. willistoni: Valente and AratIjo, 1986; and for D. nasuta: Kumar and Gupta, 1988. When more than two gene arrangements that overlap occur, they can be treated as "alleles" and it is still possible to identify the different heterozygotes but again it may be difficult to distinguish among homozygotes. In this case, however, one can estimate each one of the allele frequencies and their standard errors.…”

Heterosis and the lack of coadaptation in Drosophila nasuta

“…Ramanagar and Ayurvedic Garden are situated on opposite sides of the river Ganges about 4 km apart. Naturally inseminated females were collected as described by Kumar & Gupta (1988a) progeny, assuming that the viability of heterozygotes is always one. Table I provides frequencies of homozygotes and heterozygotes in intra-and interpopulation crosses and the relative viabiities of three karyotypes of D. nasuta.…”

Concentration of chromosomal aberrations on chromosome 3 of Drosophila nasuta

“…Of 85 inversions detected, eight are on the X chromosome, 24 are on chromosome 2, and the remaining 53 are concentrated on chromosome 3 (Kurnar & Gupta, 198 6a, 1988). Moreover, only three inversions, IIL-2 on the left arm of chromosome 2 and 111-2 and 111-35 on chromosome 3, are shown to be heterotic in both laboratory and natural populations of the species (Kumar & Gupta, 1988, 1989.…”

“…plement of this species consists of four pairs of chromosomes: a pair of metacentrics (chromosome 2), a pair of large rods (chromosome 3), a pair of dots (chromosome 4) and a pair of small rods representing the X chromosomes while the Y chromosome is submetacentric (Kumar & Gupta, 1988). Cytologically, the species is highly polymorphic and harbours a total of 85 inversions and three chromatin band deletions in natural populations examined across its distribution range (Rajasekarasetty et a!., 1979;Wakahama & Kitagawa, 1980;Kumar & Gupta, 1986a,b, 1988.…”