Question

Three genes in fruit flies affect a particular trait, and one dominant allele of each gene is necessary to get a wild-type phenotype. What phenotypic ratios would you predict among the progeny if you crossed triply heterozygous flies?

Multiple Choice

• 27:64

• 9:23

• 37:64

• 1:3

• 27:37

• 3:5

• 1:7

Would the answer be 27:37 wild to mutant?

Answer 1

The answer would be from the cross

is 27:37 wild to mutant.

If the both alleles of particular trait are recessive then the mutant organism is seen and if one dominant allele is present of particular trait then the wild type strain is observed.

Suppose if a cross is done between heterozygous flies AaBbCc x AaBbCc the following alleles are produced

ABC,ABc,AbC,Abc,aBC,aBc,abc and abC.

In the above punnett square all green box flies are wild type as they have at least one dominant allele of each trait while the rest of flies in red box are mutant as they have homozygous recessive alleles for at least one trait.