Additive genetic variance

A factor analysis of the results yielded 39 first-order and 11 second order factors. The mean intraclass correlations for the three groups of twins are shown in Table 2. The heritability estimate for the 50 factors is highly consistent across methods the MZA direct estimate is (.42) and the estimate based on reared together twins is. 52. In this instance we found evidence for non additive genetic variance for only a few measures. 

Pomiankowski I would like to comment on David Houle s pessimistic view. I don t think we need to be so pessimistic, for two reasons. If you are interested in the genetic structure of g in the current human population, you want some internal comparison. It may be that has a very high additive genetic variance today and this can be ascertained by comparison with other traits, for instance other psychological traits. Perhaps they have different additive effects. This may tell us... 

Fisher s fundamental theorem (1958) states that selection removes additive genetic variance, and thus should diminish narrow sense heritability. Because of Fisher s argument (which is mathematically correct), scientists have argued until recently that additive heritability was prima facie evidence that the trait was evolutionarily neutral (e.g. Tooby Cosmides 1990). Flowever, the ubiquity of additive genetic variation, even for traits subject to strong selective forces, has forced evolutionary biologists to try to account for the routine violations of Fisher s fundamental theorem. 

In a heritability study using parent-offspring regression for the levels of fhiit proanthocyanidins, the heritability estimates (I ) were significantly positive (A =0.43), indicating significant additive genetic variance exists for proanthocyandin Suit levels. 

While tau mutations have provided an important piece in the puzzle of FTD genetics, they probably account for less than 50% of the genetic variance in familial FTD [64]. However, the successful identification of additional contributing genetic factors largely depends on the development of precise phenotypic classification schemes, which... 

Table 3. Median proportions of variance attributed to additive genetic, nonadditive genetic, shared environmental, and nonshared environmental effects plus error and broad heritability, derived from eight kinships, for seventeen brief strong vocational interest blank scales...

HERITABILITY A concept that quantifies the proportional contributions of genotype and environment to some trait broadly, the proportion of the phenotypic variance in a population that is attributable to genetic differences among individuals in the population narrowly, the proportion of the phenotypic variance that is attributable to additive genetic variability (i.e., the proportion of phenotypic deviation from the population mean that is transmitted to the next generation). 

Gangestad You don t need a lot of dominance variance to get inbreeding depression on a trait, if most of the trait s genetic variance is due to mutations. With rare mutations there are very few double recessive mutations, and therefore, almost all of the variance caused by each mutation is merely additive, even if the effect of double recessives is nonadditive. So rare mutations can produce low dominance variance yet substantial inbreeding depression. 

FIG. 1. Means and standard errors of the coefficient of phenotypic variance (CVP), the coefficient of additive genetic variation (CVA) and the coefficient of residual variation (CKR). Comparison is made between paired data for sexual and non-sexual characters from the same species (Data from Pomiankowski Mpller 1995, n = 16). 

Pomiankowski I think it was naive to believe the lek paradox as formulated— that there will be no genetic variance. This has been shown to be wrong. What explains the existence of variance and if it happens to be higher in sexual traits is a matter for experimental investigation. The fact that both sexual traits and g may share high additive variance may have no significance, since these may have completely different explanations. 

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