There are 3
exclusive mutually birth orders that could
make two
affecteds and 1 unaffected - unaffected child first born, unaffected child
second born,
and unaffected child third born. Thus, there is a 3/64 + 3/64 + 3/64
= 9/64
chance that 2 out of 3 children will be affected.
The correct answer is B. The parents are heterozygous with polka-dot tails, so they both have Pp genotype. The combination of their genotypes (Pp x Pp) could produce 4 genotypes PP, Pp, Pp and pp. Therefore, there is 25% chance for a PP genotype, 25% for a pp genotype and 50% for a Pp genotype. The PP and Pp genotypes produce a polka-dot tail phenotype and the pp genotype produces a solid coloured tail phenotype. In conclusion, there is 75% chance for a polka-dot tail (25% for a PP + 50% for a Pp) and a 25% for a solid coloured tail phenotype (25% for a pp).
