An experimental method for evaluating the contribution of deleterious mutations to quantitative trait variation

Abstract

SummaryUnconditionally deleterious mutations could be an important source of variation in quantitative traits. Deleterious mutations should be rare (segregating at low frequency in the population) and at least partially recessive. In this paper, I suggest that the contribution of rare, partially recessive alleles to quantitative trait variation can be assessed by comparing the relative magnitudes of two genetic variance components : the covariance of additive and homozygous dominance effects (C ad ) and the additive genetic variance (V a ). If genetic variation is due to rare recessives, then the ratio of C ad to V a should be equal to or greater than 1. In contrast, C ad \V a should be close to zero or even negative if variation is caused by alleles at intermediate frequencies. The ratio of C ad to V a can be estimated from phenotypic comparisons between inbred and outbred relatives, but such estimates are likely to be highly imprecise. Selection experiments provide an alternative estimator for C ad \V a , one with favourable statistical properties. When combined with other biometrical analyses, the ratio test can provide an incisive test of the deleterious mutation model.

The Effect of Antagonistic Pleiotropy on the Estimation of the Average Coefficient of Dominance of Deleterious Mutations

“…It is also clear from Table 7 that the regression estimate b y.x increased toward the south whereas the estimate 1/b x.y always showed large values. Another useful parameter to be compared among these populations is the variance among genotypic values for homozygous chromosomes, V H , because the ratio V A /V H is expected to be low under a mutation-selection balance model and large under balancing selection (Charlesworth and Hughes 1999;Kelly 1999). In fact, as stated above, the value of ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi V A =2V H r ffi s y =s x is an estimator of the average h with a mutation-selection balance expectation analogous to that of ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi b y:x 3 ð1=b x:y Þ r and h DL .…”

Effects of inbreeding on population mean performance and observational variances in Eucalyptus globulus

“…The magnitude ofσ 2 f(self) relative toσ 2 f(pol) may depend on the genetic mechanisms underlying inbreeding depression. Results from several studies have indicated that the betweenfamily variance in selfed progeny is expected to be substantially greater than that in outcross progeny when inbreeding depression is caused by the expression of rare deleterious alleles in homozygous individuals (Kelly, 1999;Moorad and Wade, 2005). In particular, Kelly (2005) studied the development of the selfed to outcross between-family variances as a function of the average dominance degree of rare deleterious alleles (h) and, for partially recessive alleles with h = 0.2, the expected ratio was about 5 when the base parents were not inbred (increasing to 10 for fully inbred parents).…”

Inbreeding and the genetic variance in floral traits of Mimulus guttatus

“…The former reflects the fact that lethals and steriles should have low population frequencies and be partially or completely recessive (Simmons and Crow, 1977). Such alleles make a greater contribution to C AD and V DI (proportionally) than do alleles with intermediate frequencies (Kelly, 1999b). Willis (1999a) found that lethals and/or steriles make a minority contribution to inbreeding depression in fitness-related traits.…”

“…Estimates for these components can then be used to test alternative models. For example, the rare recessives model predicts that C AD should generally be greater than V A , and that V DI may be three or four times greater than V A (Kelly, 1999b). Various epistatic models may also produce specific predictions for the expected resemblance of different classes of relatives.…”