Question

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.

Answer 1

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

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

Step-by-step 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.