Question

Tim and Stephanie are devasted when they find out their newborn son has hemophilia - a sex-linked recessive disease. Tim is shocked because he doesn’t have hemophilia, and figures if his son has it he would have gotten it from him. Is Tim correct in his thinking? Explain. Also explain what their genotypes must be in order for neither of them to have the disease but have a son who does. Be sure to include a Punnett square to support your answers.

Answer 1

Tim is thinking wrong that his son got haemophilia from him because it is a X- linked recessive trait and he contributed only Y chromosome, Stephanie is a carrier and passed the trait to his son.

The genotype of Tim = Yh, Stephanie is
`H^(c)`h

the cross resulting in
`H^(c)`Y is haemophilic that is Tim's son.

Step-by-step explanation:

genotype of Tim =

genotype of Tim's wife =

Haemophilia is a X- linked recessive trait. The son get this trait from the mother as X chromosome is passed on by her, father contributed Y chromosome to the son. Hence Tim's thought that he gave him the disease is not right.

The mother is a a carrier. This trait she must have inherited from her father as blood clotting gene on mother's X chromosome is dominant and she became carrier.

The genotype of

Tim = hh

Stephanie =
`H^(c)`h

The punnet square is shown as

`H^(c)` h

Y
`H^(c)`Y hY

h X
`H^(c)`h hh

The X chromosome from the mother which was carrier is passed on to the son, who will have defective gene for blood clotting hence haemophillic.