Long-term selection for a quantitative character in large replicate populations ofDrosophila melanogaster: II. Lethals and visible mutants with large effects

Abstract

Lethal frequencies on the second and third chromosomes were estimated three times in six replicate lines of Drosophila melanogaster selected for increased abdominal bristle number, at G 14-16, G 37-44 and G 79. Ten lethals were detected at a frequency of about 5 % or higher at G 14-16, of which only one recurred in subsequent tests. Another ten lethals which had not been detected previously were found at G 37-44, and the 5 most frequent ones recurred at G 79. In the last test, 15 presumably new lethals were detected, of which at least 4 appeared well established. In addition, six reversions (from sc to sc+), a new mutant at the scute locus and sea were discovered. The effects on the selected character of some lethals and visible mutants were large and variable, but not always sufficient to explain the observed frequencies. The major lethals detected at G 37-44 and G 79 for the first time were most probably 'mutations' (in the broad sense) which occurred during selection. The likely origins of such ' mutations' were discussed, with a suggestion that the known mutation rate for recessive lethals would not be incompatible with the observed frequency of occurrence of the 'mutations'.

Polymorphic Genes of Major Effect: Consequences for Variation, Selection and Evolution in Arabidopsis thaliana

“…However, many of these experiments report only data on the selected phenotype (e.g., bristle number) or, alternatively, the selected phenotype and some measure of fitness (e.g., Frankham et al 1968, Yoo 1980bCaballero et al 1991;Mackay et al 1994;Fry 1 et al 1995;Nuzhdin et al 1995;Zur Lage et al 1997), making it difficult to infer how a mutation will affect variation, covariation, selection, and evolutionary responses for a suite of traits that might affect fitness themselves. One approach is to document how variation at individual genes of major effect affects the genetic variance-covariance matrix (''G matrix'';Lande 1979), which represents the additive genetic variance and covariance between traits.…”

Within-Generation Mutation Variance for Litter Size in Inbred Mice

“…Direct evidence of new mutations with large effects in experimental selection lines was initially reported during the second half of the 20th century (Macarthur 1949;Yoo 1980;Bradford and Famula 1984). The mutational input of genetic variance per generation (s 2 m ) can be viewed as the ultimate source of polygenic variation and thus as the raw material for the maintenance of genetic variability in populations (Hill 1982a (Lynch 1988;Houle et al 1996).…”

Inbred mouse strains and genetic stability: a review

“…As ironically suggested by Bailey (1982), entropy is inescapable, even for genes. The importance of new mutations in experimental species has been suggested by several investigators in recent decades, with reports of new mutations with large effects (Yoo, 1980;Bradford and Famula, 1984) and infinitesimal polygenic mutation variances (Caballero et al, 1991;Keightley, 1998). As a whole, mutation is a powerful source of allogenicity in inbred strains.…”

“…Single mutations with large phenotypic effects in inbred strains of mice provided the first evidence of their vulnerability to mutation (Lord and Gates, 1929;Yoo, 1980) and, controversially, they have been a major source of new inbred strains. Taking mouse coat color as an example, reports of new mutants were common in the scientific literature during the mid-20th century (Cloudman and Bunker, 1945;Dickie, 1954 andLoosli, 1963;Pierro and Chase, 1963;Wolfe and Coleman, 1964), and they are still arising in experimental stocks worldwide (see Table 1).…”