Experiments on the physiology and genetics of the smut fungi. Cultural characters. Part II. - The effect of certain external conditions on their segregation

Abstract

The researches, which are described under the above general heading, were begun in 1925. Their object was to find out if the inheritance of the characters in the smut fungi was similar to that in the higher plants and animals. The evidence presented, and to hand, was in the previous paper (1928) considered sufficient to justify the conclusion that, in their segragation, these fungi did obey the laws of meendel. In that paper certain of the cultural characters were shown to be segregated in ratios of 2 : 3, 3 : 1 and 4: 0 in those cells which were deduced to be the immediate progeny of the reduction divisions. The anomalous ratio of 3 : 1 was at that time the only difficulty, and this was, it seemed, probably due to the interaction of a number of Mendelian factors. Since that time segregation ratios of 2 : 1 : 1 (or 1 : 1: 2) and 1 : 2 :1 have been recognised. It is thought that the conclusion that the segregation in these fungi is along Mendelian lines is fully justified by the experiments described in this paper. In the fungi generally, as Brierley has stated (1929), "local peculiarities" may be expected, but, so far, in the smut fungi I find typical haploid inheritance with one possible exception. If the factor gender (sex) only is considered, the evidence is overwhelmingly in favour of strict Mendelian segregation, both in that the factors are segregated in pairs and, as demonstrated in the present paper, that segregation under normal circumstances is haphazard. Also when the cultural characters are considered, the evidence is conclusive expect that in one character this peculiar 3 : 1 ratio is found.