Solved Family pedigree practice problems For questions 1-2 | Chegg.com - Free Printable

Problem Analysis:

We are given a family pedigree and asked to determine the mode of inheritance, the genotypes of individuals II-3 and III-1, and the probability that they would have an affected son. Let's break this down step by step.

#### Step 1: Analyze the Pedigree
The pedigree shows:
- Individual I-1 (male) is affected (black square).
- Individual I-2 (female) is unaffected (white circle).
- Their offspring:
- II-1 (male) is unaffected.
- II-2 (female) is unaffected.
- II-3 (male) is unaffected.
- II-4 (female) is unaffected.
- II-5 (female) is unaffected.
- II-6 (male) is unaffected.
- The next generation (III):
- III-2 (male) is affected.
- III-6 (male) is affected.
- All other individuals in generation III are unaffected.

#### Step 2: Determine the Mode of Inheritance
To determine the mode of inheritance, let's consider the key features of the pedigree:
1. Affected Individuals: Only males (III-2 and III-6) are affected.
2. Pattern of Transmission:
- The affected trait skips generations.
- Affected individuals (III-2 and III-6) have unaffected parents.
- There is no clear pattern of dominant or recessive inheritance in autosomal traits.
- The trait appears to be linked to the Y chromosome, as only males are affected and the trait is passed from father to son.

Given these observations, the most likely mode of inheritance is Y-linked. Y-linked traits are carried on the Y chromosome and are therefore passed from father to son only. This explains why only males are affected and why the trait skips generations when it is not passed to a male offspring.

#### Step 3: Determine Genotypes
- Individual II-3: Since II-3 is unaffected and Y-linked traits are only expressed in males, II-3 must have the normal allele on his Y chromosome. Therefore, his genotype is Y^N (where Y^N represents the normal allele on the Y chromosome).
- Individual III-1: III-1 is unaffected and female. Since Y-linked traits are only relevant to males, her genotype is irrelevant to the Y chromosome. However, for completeness, we can say she has two X chromosomes, but her genotype with respect to the Y-linked trait is simply that she does not have a Y chromosome. Thus, her genotype is XX (normal).

#### Step 4: Probability of Having an Affected Son
- Individual II-3: Since II-3 has the normal allele on his Y chromosome (Y^N), any sons he has will also inherit the normal allele on their Y chromosome. Therefore, the probability that II-3 would have an affected son is 0.
- Individual III-1: III-1 is female and cannot pass a Y chromosome to her offspring. Therefore, the concept of having an affected son does not apply to her. The probability is 0.

Final Answer:

1. Mode of Inheritance: Y-linked
2. Genotype for II-3: Y^N
3. Genotype for III-1: XX
4. Probability that II-3 would have an affected son: 0
5. Probability that III-1 would have an affected son: 0

$$
\boxed{\text{Y-linked, Y^N, XX, 0, 0}}
$$