Chromosome IV in Drosophila is a very small chromosome and carries a tiny amount

Question

Chromosome IV in Drosophila is a very small chromosome and carries a tiny amount of genetic material. Fruit flies that are trisomic for chromosome IV have no apparent phenotypic abnormalities, andtheyretaintheirfertility. AmongthegenesonchromosomeIVisoneforwhicharecessivealleleey produces the “eyeless” phenotype. A male that is trisomic for chromosome IV and has the genotype + eyeyiscrossedtoadiploidheterozygousfemale. Assumingthatrandomsegregationofchromosomes takes place during spermatogenesis, and that all sperm are viable, what proportion of offspring will be trisomic and eyeless?

A. 1/12

B. 1/6

C. 1/4

D. 1/3

E. 1/2

Explanation / Answer

Option C is correct. Since out of four phenotype combination two will be trisomic and out of which one will carry dominat and one will carry recessive. Only trisomic reccesive are eyeless.

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