Question

Two people with PSACH (dominant, homozygous lethal) marry. Her family are not bald even in old age, but she is color blind (x-linked recessive). His family all have normal color vision and both of this parents have full heads of hair. However, he is bald. What is the probability that their first son will be of normal height, color blind and bald?

the answer is 0.167, how do you get there?

Answer 1

According to my knowledge,the question given is wrong. Why?

1.PSACH is an autosomal dominant inherited disease,i.e. if 2 person having PSACH marries, there is no chance that any of their children will have normal height. Either they will have PSACH or they will be a carrier.So, no normal height.

Note: Even if a child gets the gene causing this disease from one parent then also he/she will be a victim as it is a autosomal dominatd inherited disease .

2.Colour blindness gene is on the X chromosome. So there is a chance that the son will be colour blind if the mother is colour blind.

3. Baldness gene is also on the X chromosome.Men usually get their baldness gene from their mother. Since the mother is not bald, but the father is , there is no chance that their son will be bald . So , No Baldness

So, the problem given may be is correct but the answer that is said to be correct is wrong .