1. Give the genotypes of the ABO blood groups for individuals 1 and 2 - AQA - A-Level Biology - Question 6 - 2022 - Paper 2

In Figure 3, individuals with a Rhesus positive phenotype (like individuals A and AB) can produce offspring with a Rhesus negative phenotype (like individual O). This indicates that the presence of the Rhesus positive allele can mask the expression of the Rhesus negative allele.

To find the probability, we assume that individual 1 is heterozygous for the Rhesus blood group (${Rr}$) and individual 2 is also ${Rr}$ (since they can produce Rhesus negative offspring).

Possible Rhesus offspring:

• ${RR}$ (Rhesus positive)
• ${Rr}$ (Rhesus positive)
• ${rR}$ (Rhesus positive)
• ${rr}$ (Rhesus negative)

This results in a probability of producing a Rhesus positive child of rac{3}{4}.

Next, consider the ABO blood groups. Individual 1 can pass on either $I^A$ or $i$, while individual 2 can pass on $I^A$ or $I^B$. The combinations yielding blood group A are:

1. $I^A I^A$ (from individual 1) and $i$ (from individual 2)
2. $I^A i$ (from individual 1) and $I^B$ (from individual 2)

Thus, the probability of individual 3 being blood group A is rac{1}{4} (for homozygous) + rac{1}{4} (for heterozygous from individual 1's contribution).

Combining these, the total probability of producing a Rhesus positive son with blood group A is:

P(RR ext{ or } Rr) imes P(A) = rac{3}{4} imes rac{1}{2} = rac{3}{8}.