12. A fly with apricot coloured eye was crossed With a septa eyed fly of opposite sex. In Fl all flies were Wild tvpe. The genes responsible for the two
(1) allelic                     (2) nonallelic
(3) pseudo-allelic     (4) paralogous genes

Detailed explanation

• Each parent is homozygous for a recessive eye-color mutation: one apricot, one sepia.

• All F1 flies are wild-type, so each F1 carries one apricot allele and one sepia allele but still shows normal color.

• This happens because each mutant provides the functional wild-type allele for the gene mutated in the other. That is classic complementation, which indicates the mutations are in different genes.

Option-by-option:

1. Allelic

• If both mutations were different alleles of the same gene (allelic) and both recessive, the F1 heteroallelic genotype (apricot/sepia) would still lack any normal allele and would be mutant, not wild type. So this is incorrect.

2. Nonallelic – correct

• Nonallelic means the mutations are in different genes. In a diploid F1, each gene now has one functional wild-type copy, so the phenotype is wild type. This matches the observed result.

3. Pseudo-allelic

• Pseudo-alleles are very closely linked genes that behave almost like multiple alleles in some tests, but the key diagnostic here is simple, full complementation to wild type, which points to independent genes, not a pseudo-allelic complex.

4. Paralogous genes

• Paralogous genes are related by duplication within a genome, a molecular evolution term, not the classical genetic relationship inferred from this cross. It does not describe the complementation test outcome.

Therefore, because the cross of two recessive mutants yields all wild-type F1, the two eye-color mutations are best described as nonallelic.