Non-allelic interactions and genetic isolation in wild populations of Aspergillus nidulans

The Inheritance of Penicillin Titre in Wild-type Isolates of Aspergillus Nidulans

“…With regard to natural variation for other quantitative characters in fungi, predominantly additive gene action, like that reported here for penicillin titre, has been found for radial growth rate, specific growth rate and growth yield in A. nidulans (Butcher, 1969;L. Handley, personal communication), linear growth rate in Aspergillus amstelodami (Caten, unpublished) and linear growth rate in monokaryons of Schizophyllum commune (Simchen, 1966a).…”

“…In haploid organisms all nonadditive variation must arise through epistasis. Comparison of the mid-parental value and the mean progeny value therefore provides a direct test for epistatic variation with a directional component (Butcher, 1969;Mather & Jinks, 1971). The deviation of the mean progeny value from the mid-parental value gives an estimate of the contribution of gene interaction effects ([i]) to the mean phenotype.…”

Use of genotype-environmental interaction analysis in the study of natural populations of Aspergillus nidulans

“…(It is realised, of course, that some form of transient heterokaryosis must take place in order that these crosses may occur.) Jinks et al (1966) and Butcher (1969) also reported that in these inter h-c group crosses, but not in intra-group crosses, a breakdown of nonallelic interactions occurred causing most of the progeny to have a reduced growth-rate when compared to the parental values. There is, therefore, clear evidence for the existence of a barrier to gene flow between h-c groups by way of heterokaryosis and the subsequent events of the parasexual cycle, and some evidence for a restriction of gene flow by way of sexual outcrossing between h-c groups.…”

“…This observation would appear to be confirmed by the analysis of continuous variation found among the progenies of individual crosses. In general, it is found that the genetical variance is significant and large if the parents of the cross belong to different h-c groups, but is not significant or is low if the parents belong to the same h-c group (Jinlcs et aL, 1966;Butcher, 1969). Thus it may be postulated that members of a single h-c group tend to be genetically similar to each other and different from isolates belonging to other h-c groups.…”

“…An examination of the genetical variance found within the progenies of crosses will reveal considerable information about the amount and nature of the difference in genotype between each pair of parental isolates (Croft and Simchen, 1965;Jinks et al, 1966;Simchen, 1966;Butcher, 1969). However, this method is inefficient in that a relatively large experiment is required in order to make a comparison of only two isolates.…”