the following pedigree shows the inheritance of an autosomal recessive condition. what are the chances that…

the following pedigree shows the inheritance of an autosomal recessive condition. what are the chances that the female in generation ii is a carrier for this condition? generation i 1 2 3 4 ii 1 2 iii 1 2 3 4 5 6 female male unaffected individual affected individual click or tap a choice to answer the question. 0% 33% 50% 75% 100%

the following pedigree shows the inheritance of an autosomal recessive condition. what are the chances that the female in generation ii is a carrier for this condition? generation i 1 2 3 4 ii 1 2 iii 1 2 3 4 5 6 female male unaffected individual affected individual click or tap a choice to answer the question. 0% 33% 50% 75% 100%

Answer

Explanation:

Step1: Determine parents' genotypes

Since the condition is autosomal - recessive and individual II - 1 has an affected child (III - 2 and III - 3), and his mother (I - 2) is affected (aa), II - 1 must be a carrier (Aa). Individual II - 2 has unaffected parents (I - 3 and I - 4) and has affected offspring, so II - 2 must also be a carrier (Aa).

Step2: Use Punnett - square analysis

The cross between II - 1 (Aa) and II - 2 (Aa) has the following possible genotypes for their offspring: AA:Aa:aa = 1:2:1. But we are interested in the non - affected individuals. Among non - affected individuals (AA + Aa), the ratio of carriers (Aa) to non - affected is 2 out of 3. Since we are only considering the female in generation II (assuming no other information to suggest otherwise), and we know from the cross of two carriers (Aa x Aa) that the probability of a non - affected individual being a carrier is $\frac{2}{3}\approx66.7%$. However, if we assume that we are just looking at the general probability of being a carrier based on the fact that one of her parents is a carrier and the other's status is unknown in a more simplistic way (ignoring the full pedigree analysis in a less accurate sense), if one parent is a carrier (Aa) and the other is assumed to be non - carrier (AA) for a quick estimate, the cross AA x Aa gives Aa:AA = 1:1, so the probability of being a carrier is 50%. In the context of the pedigree, if we consider that the parents of II - 2 are both likely non - carriers (but have passed on the recessive allele to their affected offspring through being carriers themselves), and we focus on the fact that II - 1 has a 50% chance of getting the recessive allele from his affected mother (I - 2) and II - 2 also has a high chance of being a carrier due to her affected offspring, a more accurate way is to consider the cross of two carriers (Aa x Aa). The probability that a non - affected individual from a cross of two carriers (Aa x Aa) is a carrier is $\frac{2}{3}$. But if we assume that we are looking at the inheritance from a single carrier parent situation (simplified), the probability that an individual is a carrier when one parent is a carrier is 50%. Since the question may be looking at a more basic inheritance from a single - carrier - parent perspective, we consider the following: Let the allele for the normal condition be A and the recessive allele for the condition be a. If one parent is a carrier (Aa) and the other is non - carrier (assumed for simplicity), the cross is Aa x AA. The possible genotypes of the offspring are AA and Aa in equal proportions.

Answer:

50%