Question

Mark and Michelle both have dark hair, which is a dominant trait. But their first child is blonde. Which is the most likely explanation

Answer 1

They are heterozygous for the dark hair.

Answer 2

Both parents have a recessive blonde allele that got passed on to their child.

Another gene caused the alleles for brown hair to deactivate.

It's not possible--Mark can't be the real father.

One of the two has a blonde allele that is dominant in the child.