Principles of Inheritance and Variation Question 88
88. When two genetic loci produce identical phenotypes in cis and trans position, they are considered to be
(a) pseudoalleles
(b) different genes
(c) multiple alleles
(d) parts of same gene
Show Answer
Answer : b
Hints & Solution
(b) Complementation test, also called cistrans test, is for determining whether two mutations associated with a specific phenotype represent two different forms of the same gene (alleles) or are variations of two different genes. During the complementation test, if a phenotype is observed when a recessive mutation is combined in trans with another recessive mutation that has been mapped to the same area, it is concluded that these mutations are alleles of the same gene; neither allele produces a product that can restore wild-type function. However, if the trans- heterozygote exhibits a wild-type phenotype, it is concluded that the two mutations are alleles of different genes; each mutant has a functional version of the other gene. The complementation test was developed by American geneticist Edward B. Lewis. If the combination of two genomes containing different recessive mutations yields a mutant phenotype, then there are three possibilities: One mutation affects the expression of the other.
