genotypes of parents and children?

Question

Two parents have four children. PHENOTYPES of the children are: 1 has type A blood, 1 has type B blood,1 has type AB blood,1 has type O blood. What are the genotypes of the parents? What are the genotypes of the children?

Answer 1

The only way to get these children is if the parental genotypes are AO and BO (or IAi and IBi, depending on the system of notation you are using.)

Figure this out from the offspring. With a child who is Type O, having alleles OO, each parent must have an O.

With a child who is Type AB, one parent must have an A and one parent must have a B.

Try the cross.
Parents: AO x BO
Gametes: A, O and B, O
Punnett square: Put A, O on the side and B, O on the top.

First row of boxes in the square: AB and AO
Second row of boxes in the square: OB and OO

These four boxes of the square are the genotypes of the children.

Answer 2

Just do two punnet squares. You know the alleles for the AB parent is I^A and I^B. This is the only possibility for AB blood types. The B parent can either be I^B and I^B or I^B and i (the O allele). Remeber that the I^A andI^ B alleles are codominant so the individual would phenotypically express both alleles if he/she has both. The O allele is always recessive and is not phenotypically expressed when paired with I^A or I^B. The only way to get an individual with an O bloodtype would be for both parents to have the O (or i) allele, so none of the children in your problem could ever have O bloodtype. Possibilities include AB, B, and A bloodtypes.