Question

Duplication of Vermillion eye colour gene leads to the expression of the mutant phenotype. Which of the following can lead to normal phenotype with this duplication present?

(a) Reverse tandem duplication

(b) Duplication of normal eye colour gene

(c) Deletion of both the Vermillion gene

(d) Translocation of Vermillion gene to another chromosome

I have been asked this question at a job interview.

This intriguing question originated from Chromosomal Abnormalities : Duplication topic in chapter Chromosomal Basis of Inheritance of Cytogenetics

Answer 1

The correct option is (b) Duplication of normal eye colour gene

The best explanation: Duplication in normal eye colour gene would balance the mutant gene product and lead to expression of wild type phenotype. Reverse tandem duplication will only create more copies of mutant making phenotype worse, also deletion of both genes will cause imbalance. Translocation makes no difference in expression unless it’s beside a heterochromatin.