Your friend Joe has a younger brother Sam and two older sisters. Sam has a strange disorder that has caused his hair to turn green. The doctor says that this is caused by a single gene that is inherited, and that boys are more likely to have green hair then girls. However Joe, his sisters, and both of his parents have normal hair color. Joe does not know much biology and is confused. Explain to Joe how his brother's condition could have arisen even though Joe has normal hair. Then discuss the likelihood that a) Joe, and b) Sam will have children with green hair. Assume that they both marry women with normal hair color. You will need to include information on meiosis and transmission of genes to assure that Joe understands. HINT: As part of your answer, indicate the percent of girls vs. boys that you predict would have green hair if fathered by Joe vs. Sam.

The correct answer is - it is due to the case of sex-linked recessive disorder.

Explanation:

It is pointed out by the doctor that Sam has a condition due to recessive allele and it is given that boys have this condition more than girls which suggests that it is a sex-linked recessive disorder. This comes from their parents but it is given that the father has normal hair which means the father has no recessive allele, then it must come from the mother even mother has not this condition but she could be a carrier for this trait.

Joe and his sister do not have this condition as they get the normal dominant allele from mother and father.

The chances of being a carrier by his sisters are 50%. If Joe marries

IF Joe marries a non-carrier woman, he will have all normal children with no green hair. IF Joe marries a normal hair color carrier women then there would 25% chances of being diseased offspring and 50% chances of being a carrier, and if women is completely normal then all offspring will be normal.

carrier woman, his children will have a 25% chance of being green-haired. A 25% chance of being

IF Sam marries a normal woman, the children will have a 25% chance of being a carrier, a 25% chance of being green-haired, and a 50% chance of being normal.