Mercy with blood group A and Brian with blood group B had three children. One child had blood group O, one had blood group A and one had blood group B. explain the pattern of inheritance by means of a genetic diagram.
Answers
this is the simplest way that I could explain.
Out of these three blood groups, O is the recessive one, which needs another same recessive gene to express itself freely.
Blood group A and Blood group B both are dominant genes and they have the capability to express themselves freely.
In the presence of a dominant trait and a recessive trait, the dominant trait will be expressed whereas in the presence of both dominant traits, both the traits (blood group in this situation) will be expressed. Recessive traits will only be able to express themselves, if both traits are recessive.
Blood group of Parents : A and B
That means
IAIi × IBIi
On crossing these we get all the possible genotypes:
IAIB, IAIi, IiIB, IiIi, IBIi
IA is the dominant trait for blood group A
IB is the dominant trait for blood group B
Ii is the recessive trait for blood group O
Now, out of these posibilities their children had blood groups :
Child with blood group O: IiIi
Child with blood group A: IAIi
Child with blood group B: IBIi