dentical twins are produced from the same sperm and egg (which splits after the first mitotic division), whereas fraternal twins are produced from separate sperm and separate egg cells. If two parents, one with brown eyes (a dominant trait) and the other with blue eyes (the recessive trait) produce one twin boy with blue eyes, what is the probability that a fraternal twin will transmit the blue eye allele to his or her offspring

50% probability

Explanation:

During copulation between male and female the genetic component of the offspring that results is 50% of the fathers gene and 50% of the mother's gene.

If a fraternal twin married a woman and they both produce a child, the father contributes half of the genetic make up while the mother contribute half of it to make up the 100% genetic combination.

For a fraternal twin father who has a blue eye, the probability of him to transfer a blue eye color gene into his child is 50%.