AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

Eye colour in drosophila

3. EYE COLOUR IN DROSOPHILA

• Another example of multiple alleles in Drosophila is eye colur.
• Wild type Drosophila have red eyes; but a vast variety of eye-colour mutants have been studied extensively.
• More than a dozen mutant alleles of one gene (white, symbolized w) results in flies with eye colour ranging from pure white through a series of intermediate colours up to nearly the wild-type red when present in the homozygous condition.
• The recessive mutant white was discovered by T.H. Morgan and C. Bridges in 1912.
• The other mutants alleles of this gene are w^a (white apricot), w^e (white eosin), w^ch (white cherry), w^co (white coral), w^col (white coloured), w^w (white wine), w^bl (white blood), w^crr (white carrot) w^cf(white coffee) etc.,
• Generally a cross between any two mutants results in the appearance of intermediate phenotype in the F1 progeny.
• The genotype appearing as wild type are w^+S/ w^+S - Stellen bush strain, w^+C/w^+C - Canton S strain and w^+G/w^+G - Graff-Reinet strain.
• The various wild type genotypes that appear as red can be quantitatively seperated.
• Such types of alleles, which act within the phenotypic range of each other, are called isoalleles.
• Many such isoalleles have been discovered at a later period.