Quantitative genetic variation induced by P transposable elements in Drosophila melanogaster

• Main Author: Lai, Chaoqiang
• Published: University of Edinburgh 1990
• Subjects: 591.35
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653610

To determine the ability of the P-M hybrid dysgenesis system of Drosophila melanogaster to generate mutations affecting quantitative traits, X chromosome lines were constructed in which replicates of isogenic M and P strain X chromosomes were exposed to a dysgcnic cross, a nondys-genic cross, or a control cross, and recovered in common autosomal backgrounds. Mutational heritabilities of abdominal and sternopleural bristle score were in general exceptionally high. P strain chromosomes were eight times more mutable than M strain chromosomes, and dysgcnic crosses three times more effective than nondysgenic crosses in inducing polygenic variation. However, mutational heritabilities of the bristle traits were appreciable for P strain chromosomes passed through one nondysgenic cross, and for M strain chromosomes backcrossed for seven generations to inbred P strain females. The new variation resulting from one generation of mu-tagenesis was caused by a few lines, with large effects on bristles score, and all mutations reduced bristle number. Among eight of these mutant lines and two additional mutant lines which occurred spontaneously during stock maintenance, the range of additive effects for both abdominal and sternopleural bristle scores are 2 to 9.5 bristles (1.2-5.0ap) in females, and 3.7 to 15.7 bristles (2.3-9.1<7p) in males. The effects of nine mutant chromosomes (the exception is line NDC(19)) on sternopleural bristle scores are similar and close to l.3fff, well within the wildtype range. The effects of mutants NDC(19) for both bristle traits, and lines DP(146) and DP(146)NAB for abdominal bristle scores, are extreme (2.53-5.53<7«) compared with the wildtype. This result supports the hypothesis that the distribution of effects of mutant genes on quantitative characters is highly variable, and possibly leptokurtic. The overall degree of dominance of all mutant X chromosomes suggests they are partially recessive, but the effect of line NDC(19) on abdominal bristle score appears completely recessive. Six of the mutant lines have similar low sternopleural bristle scores of about 15, are caused by allelic mutations with a map distance of approximately 24.7 cM, 4.7 cM from the cflocus. Deficiency mapping shows they are within chromosomal bands 8A4-8C6 Lines NDC(19) and DP(146) have extremely low abdominal and sternopleural bristle scores of 11.5 and 14.9, and of 10.3 and 12.5 respectively, and map closely linked to the y locus. The test of allclism and deficiency mapping indicate they are closely linked but at separate loci within chromosomal bands !B2;lB4-6 and 1B4-6;1B10, respectively, with some epistatic effects. They are apparently single mutant alleles with pleiotropic effects on both bristle traits and viability. The mutation of line NDC(19) is probably at the scute locus. In situ hybridization analysis suggests these two mutants are associated with insertion of P elements within chromosomal region 1A-1B10, but the other six mutants probably resulted from excision of P elements at the site of 8C.