# A RH negative father has a RH negative son. What is the possibility of other children being RH negative? May we then conclude that the son's mother is also negative?

Sep 29, 2017

It all depends on the genes carried by the mother. If the mother is double recessive, all children become negative; but in this case, son's mother may not be negative.

#### Explanation:

Having a positive blood type is determined by the presence of the RHD gene, which encodes for the Rh D Antigen on the surface of Red Blood Cells. If that antigen is not present (due to defective genes), then the person has a negative blood type.

The RDH gene is present in 2 copies in our genes. However, just 1 copy is enough to have the Rh D Antigen and have a positive blood type. And vice versa, you would need to have both 2 copies of the genes to be defective in order to be negative blood typed.

So in this example, the father is $R h \left(-\right)$, meaning that he has 2 defective copies of the RHD gene. And the same goes for his son, who is $R h \left(-\right)$ as well.

• From this information, we can conclude that the mother has at least 1 defective gene out of her 2 copies. So if the other copy is defective as well, then she would be $R h \left(-\right)$ and hence, all their children will be $R h \left(-\right)$.
• However, if the mother's other copy of the RHD gene is NOT defective, then it means she is $R h \left(+\right)$ and hence there is the chance that she might pass on this working gene to their second child, making that new child $R h \left(+\right)$.

This can be summarized by this illustration: