Partitioning of variance and estimation of genetic parameters for various bristle number characters ofDrosophila melanogaster

Abstract

Phenotypic variance for each of several bristle number characters (abdominal, sternopleural, second and third coxal) was partitioned using both hierarchal and dialled designs. Heritabilities and genetic correlations were estimated from parent-offspring regressions and correlations and half-sib correlations.A high proportion of the genetic variance for abdominal bristle number was due to epistatic and sex-linked gene action, but most of the genetic variance for the other characters was additive autosomal.The genetic correlations among sternopleural, and second and third coxal bristle numbers were all high, but that between abdominals and sternopleurals was low, while those between abdominals and either second or third coxals were virtually zero. An appreciable proportion of the covariance between abdominal and sternopleural bristle numbers was non-additive genetic.The diallel method gave more reliable estimates of genetic parameters when non-additive or sex-linked genetic variation was present.

The quantitative genetics of sexual dimorphism: assessing the importance of sex-linkage

“…The three predictions can be addressed by apportioning the phenotypic variance into its genetic and environmental components and then further partitioning the genetic variance into additive, dominance, sex-linked and maternal effects. One method of estimating X-linked genetic variance utilizes multiple reciprocal crosses between inbred lines, a design known as 'the diallel cross' (Griffing, 1956;Sheridan et al, 1968;Lynch and Walsh, 1998). The diallel method permits the partitioning of trait variance into additive genetic, dominance, reciprocal and environmental variances.…”

“…For example, to estimate sex-linked effects on bristle number in D. melanogaster, Sheridan et al (1968) used a complex diallel cross in which they necessarily assumed no sex-linked dominance effects and no maternal effects other than those produced as a result of sex-linkage. Zhu and Weir (1996) solved the latter problem by deriving a method to partition the phenotypic variance (V P ) into…”

“…However, the diallel cross approach remains limited in its application because the production of inbred lines is not practical for most Cowley et al (1986) and Cowley and Atchley (1988) used an alternative approach, a half-sib design, to estimate the sex-linked variance for a series of morphological traits in D. melanogaster. As their design utilized only one or two offspring per full-sib family, they had to assume, like Sheridan et al (1968), no dominance variance and no maternal effects. As noted above, the contribution of dominance variance is a key prediction of the theory and it should not be assumed to be absent.…”

Correlation Between Bristle Systems in Drosophila Melanogaster

“…Heritabilities and genetic correlations were estimated by several methods (Sheridan et al 1968), and for most characters the estimates varied considerably between methods of estimation. This variation was attributed to a combination of sex linkage and sampling effects.…”

“…It is not clear why second coxals were involved in both cases of poor agreement between estimated and realized genetic correlations. There were few classes for this character so base population estimates of genetic parameters may have been inaccurate (Sheridan et al 1968). Realized genetic correlations of individual lines varied widely for single-trait lines (they could not be estimated in the individual two-trait selection lines).…”