In humans, Rh + blood is dominant to Rh-. A man and woman are both Rh+, but their first child is Rh-.

a) What is the chance that their next child will be Rh-?

b) Calculate the probability that the next child will be an Rh + girl.

a) There is a 25% chance that their next child will be Rh-.

b) There is a 3/8 chance for a Rh + girl

Explanation:

As we know from the question that Rh is a dominant gene. A person having only one allele for the gene will show its effect as it is the dominant character.

This means that for a person to lack the Rh factor, it shall not have any allele with the Rh factor.

To illustrate the result, lets draw a punnet square:

Rh + Rh-

Rh + Rh+/Rh + Rh+/Rh-

Rh - Rh+/Rh - Rh-/Rh-

For the probability for it to be a girl, we know that there are 50-50 chances for the next baby to be a boy or a girl. The chance of being Rh + are 75% for the next baby.

Hence,

3/4 multiplied by 1/2 is 3/8, which is the chance for the next baby to be a girl with Rh + factor.