Question

Both of tim's parents have brown eyes, but tim has blue eyes. how is this possible? choose the best answer.

Answer 1

If Tim has blue eyes, then both of his parents are heterozygous for the brown eye trait.
Here would be the alleles:
BB-Homozygous Dominant for brown eyes
Bb-Heterozygous for brown eyes
bb-Homozygous Recessive for blue eyes

If you input the heterozygous allele for brown eyes into a punnet square, you would get a 25% chance of homozygous brown eyes, 50% chance of heterozygous brown eyes and a 25% chance of homozygous recessive blue eyes. Tim is that 25% that received a trait for blue eyes.

Answer 2

where are the choices?

the answer could be that both parents are carrying the heterozygous genes. so let's say B is the dominant brown eye gene and b is the recessive blue eye gene. both parents could possess the Bb genotype, and hence by using test cross, Tim was that 25% chance where a child could inherit the bb genotype to have blue eyes