Regular responses to selection 3. Interaction between located polygenes

Abstract

1. This paper describes further investigations of the high sternopleural chaeta-number lines of Drosophila melanogaster established by directional selection by Thoday & Boam (Genet. Res. 2, 161). The lines are vg 4 with a mean of 35·6 and vg 6 with a mean of 39·2 chaetae per fly.2. Two locatable polygenes, 3a and 3b, distinguish the line third chromosomes from those of Oregon inbred (mean about 20·5, an ancestor of all the lines). These two genes are both located between the markers h and eyg and do not interact.3. There is one locatable polygene at 41·1 ± 1·7 centiMorgans distinguishing the line second chromosomes from those of Oregon. There is no evidence that this gene is a linked complex, and, if it be a linked complex, it is unlikely to occupy more than 2 map units of the second linkage group. It interacts strongly and positively with the gene 3a.4. These three genes account for 80% of the genetic variance of the vg 4 × Oregon F2.5. Two separate regions at 2·4 ± 0·5 and 50·5 ± 0·9 centiMorgans distinguish the vg 6 × chromosome from that of Oregon. They do not appear to interact. Together they interact strongly and positively with gene 3a.6. These five genes account for 87·5% of the chaeta-number difference between vg 6 and Oregon.7. The locatable polygenes on chromosomes II and III each have qualitatively distinguishable developmental effects.8. It is pointed out that, though the genetics of these lines may be unusually simple, the results indicate that attempts to locate specific genes and study their individual effects should be made more often by students of continuous variation. Since the location of the polygene in chromosome II was done using marker genes 45 map units apart, such studies may be practicable even in species whose linkage groups are much less well marked than those of Drosophila melanogaster.

Use of naturally-occurring enzyme variation to detect and map genes controlling quantitative traits in an interspecific backcross of tomato

“…Since the contribution of the entire genome is observed simultaneously, tests for epistatic interactions between QTL would be straightforward. The results presented here as well as those of many other researchers (e.g., Spickett and Thoday, 1966;Fasoulas and Allard, 1962) reveal that interactions between discrete QTL are common. In contrast, it is obviously difficult to establish the extent and nature of such interactions if only a few marker genes are segregating simultaneously-the usual situation with morphological markers.…”

Estimation of epistasis in doubled haploid barley populations considering interactions between all possible marker pairs

“…The importance of epistasis has been suggested in numerous classic quantitative genetics studies (Spickett and Thoday 1966;Falconer 1981;Mather and Jinks 1982;Pooni et al 1987;da Silva Guimarães et al 2010). Epistasis as an important genetic basis of complex phenotypes has also been revealed in several recent QTL mapping studies Yu et al 1997;Ma et al 2005;Liu et al 2011;Rahman et al 2011;Borràs-Gelonch et al 2012;Krajewski et al 2012).…”

Maximum likelihood estimation of linkage between a marker gene and a quantitative locus

“…Mather (1957, 1960) investigated the distribution of polygenic activity affecting chaeta number and viability characters along chromosome III of Drosophila melanogaster by using appropriate mutant loci on the same chromosome as genetic markers. In a series of fundamental studies, Thoday and his colleagues showed how major mutants can be used to identify, map and evaluate individual loci affecting quantitative traits (Thoday, 1961(Thoday, , 1979Spickett and Thoday, 1966;Thoday et a!., 1964). Since then this method has been applied in basic studies of biometrical or quantitative genetics of various organisms such as in Drosophila (Williams, 1968(Williams, , 1977(Williams, , 1978(Williams, and 1980Davies and Workman, 1971;Davies, 1971;Dominguez and Rubio, 1986;Shrimpton and Robertson, 1988a, b), in wheat (Patterson et a!., 1968;Law, 1966), in maize (Edwards et al, 1987) and in tomato (Tanksley and Rick, 1980;Weller, 1987;Weller et al, 1988).…”