Question

In a wild-type fungus, protein E (encoded by the haplosufficient gene “E”) normally homodimerizes, and the E-E dimer catalyzes a biochemical reaction necessary for the production of a dark pigment. ED represents a mutant, dominant, negative allele of gene E. What is the predicted phenotype of a fungus cell of genotype E+/ED, and why?

A) mutant (no pigment production), as E is haplosufficient
B) mutant (no pigment production), as no E-E dimers will form in the heterozygous

C) mutant (no pigment production), as the mutant allele ED is dominant (correct answer. why??
D) wild type (normal production of the dark pigment), as ED is a negative allele
E) wild type (normal production of the dark pigment), as E is haplosufficient

Answer 1

In a wild-type fungus, haplosufficient gene encoding protein E undergoes dimerization, that is able to produce a dark pigment. However, haplosufficient gene refers to situations where a single copy of a functional gene has the ability to maintain normal function, and remains undented even after the cells make defected proteins. Moreover, ED mutant that is dominant and negative allele,which leads to dominant negative mutation in a dimeric membrane receptor, resulting in a truncation of the cytoplasmic domain (a part of signal transduction mechanism). Primarily,phenotypic characters of a species depend upon the allele that is dominant, and ED is dominant and negative allele in this case. Therefore phenotype of a fungus cell (having genotype E⁺/ED) will be mutant type with no pigment production.