The genetic analysis we have described so far has dealt with functional genes. In these, the detection of a difference in genotype depends on the functional expression of the genes concerned. Recognizing a white-spored mutation as a character distinct from the black spore phenotype obviously depends upon the function of the gene or genes that control pigmentation, but it is also dependent on the expression of all those other gene functions that contribute to sporulation. Unless the culture can be encouraged to sporulate, the spore color cannot be scored.Even though the mutated pigmentation gene is present in every nucleus its presence can only be scored in the specific cell type in which it is expressed. The fact remains, however, that the pigmentation mutation is represented in the genotype of the organism at the DNA level. The white-spored DNA must have a different sequence to the black-spored DNA. If that difference in DNA sequence could be detected directly using recombinant DNA technologies, then the resultant molecular markers would be scorable in DNA from any nucleus of the organism, quite independently of the functioning of the pigmentation gene.
KeywordsTransposable Element Aspergillus Nidulans Agaricus Bisporus Restriction Fragment Length Polymorphism Restriction Phenotype
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