BIO333 Genetics InClass Exercise 3 Spring 2016 4 Problem 638

BIO-333: Genetics In-Class Exercise 3 Spring 2016 4. [Problem 6.38] A.C. Stevenson and EA. Cheeseman studied deafness a family in Northerm Ireland and re to following pedigree Stevenson and cheeseman. 1956. Annals ofHuman Genetics 20:177-231) a If you consider only generations Ithrough III, what is the most likely mode ofinheritance for this type of deafness? b. Provide a possible explanation for the cross between III-7 and III-9 and the results for generations IV through V 2 3 4 5 6 7 8 9 10 11 12 13 14 10 11 12

Solution

a). The answer is not x-linked recessive inheritance as one of the major patterns for X-linked recessive inheritance is that most of the affected individuals are males, but as we see in this pedigree, there has been no such selection on the basis of sex.
This pedigree shows an inheritance pattern which is autosomal recessive. As we see that there are 100% affected children for affected parents (in I-3 and I-4 and II-10 and II-11). The parents in 1st and 2nd generations, who are not affected , produce offsprings , almost half of which are affected. Secondly, there are almost equal number of males and females, therefore, no sex bias. Third, since the parents are not affected, it is an indication that the trait has skipped a generation.


b) For the results for generations 4 and 5,
Since, both the parents are affected, all the offsprings of generation 4 will be affected. Therefore, IV-1, IV-3, IV-4, IV-6, IV-7, IV-8 will be affected. Since IV-3 and IV-6 are affected and mating with IV-2 and IV-5, unless stated otherwise, we can consider that these individuals are unaffected. If they are unaffected, then none of the children would be affected as they would turn up to be carriers.
If individuals IV-2 and IV-5 are carriers, i.e. they are unaffected but heterozygous, then one child from each mating would be affected.

A possible explanation for mating between III-7 and III-9 cannot be provided.