Question

Tirst) SID: Section: 2. ABO Blood Type (20 Points) A human pedigree is shown below. The ABO blood types of some of the members of the family are shown. IV A. For the individuals listed below, circle their correct genotype. If there is more than one possible genotype, then circle all of the possibilities. Individual Possible Genotypes 1-2 IAJA AJB BIB IA; IB; II-3 IAJA AB BIB JA; III-3 IALA JAIB IBIB Ai IB; IV.1 IAA AB Biв IA B B. What is the probability that IV-1 will have blood type O? Show your calculations. Ві ii

Answer 1

A.

Individual I-2:

We do not know individual I-2's blood group. However, her son, II-2 has the O blood group which means I-2 must have an 'i' allele. Now, Individual III-4 has the blood group A. However, her father II-4 has the blood group B. Therefore, III-4 must have inherited the A allele from II-3, who also would have at most one I^A allele.

Therefore, the genotype of I-2 is I^Ai.

Individual II-3:

As we already deduced, Individual II-3 must be either of blood group A or AB. Therefore, The possible genotypes of II-3 are I^Ai and I^AI^B.

Individual III-3:

Individual III-3 could inherit either the 'i' allele or the 'I^B' allele from II-4. Since we do not know the genotype of II-3, III-3 could inherit either I^A or I^B or 'i' from II-3.

The possible genotypes for III-3 are I^AI^B, I^BI^B, I^Bi, I^Ai, ii

Individual IV-1

Given the possible genotypes of III-3, IV-1 can inherit either I^A or I^B, or i allele from III-3. Individual III-2 either has the genotype I^Ai or I^Bi.

Therefore, the possible genotypes for IV-1 are: I^AI^A, I^AI^B, I^BI^B, I^Bi, I^Ai, ii

B.

Individual IV-1 will have the O blood group when he inherits the i allele from both III-2 and III-3. Now, III-2 definitely has an i allele as her father (II-2) has the O blood type. Therefore, the probability of IV-1 inheriting the i allele from III-2 = 1/2

We know that Individual II-3 inherited the I^A allele from I-2. Therefore, the probability that II-3 has the i allele is 1/2, if she inherited the i allele from her father. So, probability that III-3 inherits the i allele from II-3 is 1/2 * 1/2 = 1/4. Additionally, the probability that III-3 inherits the i allele from II-4 is 1/2, as II-4 has one i allele.

Therefore, the probability that III-3 has the i allele is 1/4 + 1/2 = 3/4

Thus,

Probability that IV-1 has the genotype ii (Blood group O)
= Probability of inheriting the i allele from III-2 * Probability of inheriting the i allele from III-3
= 1/2 * 3/4 * 1/2 = 3/16