4. Using the pedigree below which depicts a rare autosomal recessive trait, Spar

Question

4. Using the pedigree below which depicts a rare autosomal recessive trait, Spartacus syndrome, answer the questions below. BOT 500 IV a. What is the probability of individual IV-2 being affected? b. What is the probability of individual IV-2 being a carrier? c. What is the probability of IV-2 being homozygous dominant? d. What is the probability of IIl-4 being a carrier? e. Why do we see a different probability for carrier status between IV-2 and III-4? f. What is the probability of IV-3 being affected?

Explanation / Answer

1. IV-2 can be RR,Rr or rr with ratio RR:Rr:rr=1:2:1. Therefore probability that IV-2 is affected is 1/4.

2. As mentioned in 1. probability of IV-2 being a carrier i.e Rr is 1/2.

3. Probability of IV-2 being homozygous dominant i.e RR is 1/4.

4. Parents of III-3 are Rr and Rr. Therefore the possibilities of III-4 are RR:2Rr:rr. But III-4 is unaffected therefore rr is not possible. Therefore the actual ratio is RR:2Rr. Therefore the probability of III-4 being a carrier is 2/3.

5. As mentioned in 4. III-4 is confirm unaffected (rr is ruled out) while IV-2 can be anything. Hence the probabilitieds are also different.

6. Parentsof IV-3 are RR:2Rr. Hence the probability of a parent passing r trait to the offspring is 1/3. That is for both the parents. For an offspring to be affected we need r from both the parents. Hence the probability of offspring being affected is 1/3 X 1/3 i.e 1/9.

Related Questions

Navigate

• Browse (All)
• Browse 4
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.