Variation of scutellar bristles in Drosophila. IX. Chromosomal analysis of scutellar bristle selection lines.

Abstract

Drosophila melanogaster, by reason of its small number of chromosomes, the lack of crossing over in the male, male hemizygosity for the 1st chromosome and the existence of inversion (dominant marked) chromosomes. provides a means of studying the chromosomal distribution of effective factors and the extent of the interactions between these factors. PAYNE (1918) used a combination of backcrossing and recombination and found that the response to selection resulted from genetic changes in chromosomes 1 and 3. In lines selected for increased abdominal bristle number MATHER (1942) found that chromosome 2 played a larger part than had chromosome 3. In the low selection lines however, the major autosomes were of approximately equal importance. SISMANIDIS ( 1942) similarly attributed the majority of the response to selection for increased scutellar bristle number to the 2nd chromosome. MATHER and HARRISON (1949) carried out an extensive assay of 12. abdominal bristle selection lines and the parents involved in producing these lines. The chaetae-producing potential of the three major chromosomes were different for each of the 12 lines. In general interaction between chromosomes 1 and 3 was favourable to the direction of selection relative to that in the unselected parent populations. The other interaction patterns however were heterogeneous. ROBERTSON (1954) and ROBERTSON and REEVE (1953) analysed the chromosomal components of lines selected for large and small size by synthesising stocks which possessed all possible combinations of chromosomes from the two lines. Selection for large body size involved changes largely in chromosome 3 (ROBERTSON and REEVE 1953), while selection for small size produced effects mainly in the 1st (ROBERTSON and REEVE 1953; ROBERTSON 1954). In the large strain, the joint action of chromosomes 2 and 3 was greater than the sum of their individual effects. The polygenic control of DDT resistance in D. melanogaster was suggested by the study of whole chromosome changes (KING and SBMME 1958). Resistance resulted from changes in all three major chromosomes but the apportionment amongst them was not the same for the two lines analysed. The subdivision of genetic changes resulting from the effects of selection ' Slipported In part by Public Health Service Research Grant GM11778 01. Taken from a dissertation submitted to the Unn?rsity of California in partial fulfillment of the requirements for the Ph D degree Present address Division of Plant Industry, CSIRO, Canberra, Australia