Feather colour in budgies is determined by two different genes, Y for pigment on the outside of the feather, and B for pigment on the inside of the feather. YYBB, YyBB, or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white. Two blue budgies were crossed. Over the years, they produced 22 offspring, five of which were white. What are the most likely genotypes for the two blue budgies?
A) yyBB and yyBB
B) yyBB and yyBb
C) yyBb and yyBb
D) yyBb and yybb

Question

Quizplus · Accepted Answer

If two blue budgies produced white offspring, it means that both parents must have carried the recessive alleles for both genes (yybb). This rules out options A and B since both have at least one dominant allele. Therefore, the only option left is C. The parents must have been yyBb and yyBb, which means that each parent passed on a y and a b allele to their offspring. The probability of producing white offspring from this cross is 1/16, which matches with the observed frequency of five out of 22 offspring.

Feather Colour in Budgies Is Determined by Two Different Genes