Pedigree Analysis worksheet 1 - 91148 Human Genetics and Precision ... - Free Printable

Problem Analysis and Solution

The task involves analyzing a pedigree chart to determine the inheritance pattern of albinism and the genotypes of specific individuals. Let's break it down step by step.

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#### Step 1: Determine whether the albinism trait is dominant or recessive.

##### Key Observations from the Pedigree:
1. Affected Individuals: The black symbols represent individuals with the albinism trait.
2. Patterns of Inheritance:
- In the left side of the pedigree, there are unaffected parents (both white squares and circles) who have an affected offspring (black circle).
- In the right side of the pedigree, there are unaffected parents who also have an affected offspring.
- Affected individuals (black symbols) do not appear to pass the trait to all their offspring.

##### Reasoning:
- If the trait were dominant, at least one parent of an affected individual would also need to be affected (since a dominant allele would express the trait). However, in this pedigree, we see unaffected parents having affected offspring, which suggests that the trait is recessive.
- For a recessive trait:
- Both parents must be carriers (heterozygous, e.g., `Aa`) to produce an affected offspring (homozygous recessive, e.g., `aa`).
- Unaffected parents can have affected offspring if both carry the recessive allele.

##### Conclusion:
The albinism trait is recessive.

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#### Step 2: Determine the genotypes for females A & B.

##### Notation:
- Let `A` represent the normal allele (dominant).
- Let `a` represent the albinism allele (recessive).

##### Female A:
1. Parents of Female A:
- Both parents are unaffected (white symbols), so their genotypes must be either `AA` or `Aa`.
- One of their children (the sister of Female A) is affected (black symbol), meaning she has the genotype `aa`.
- For an `aa` child to be produced, both parents must be carriers (`Aa`).

2. Genotype of Female A:
- Since Female A is unaffected (white symbol), her genotype must be either `AA` or `Aa`.
- However, since both her parents are `Aa`, there is a chance she could be either `AA` or `Aa`. To determine this precisely, we need more information, but based on the available data:
- Female A could be either `AA` or `Aa`. Without additional information about her offspring or other relatives, we cannot definitively say which one.

##### Female B:
1. Parents of Female B:
- The father is affected (black square), so his genotype is `aa`.
- The mother is unaffected (white circle), so her genotype must be `Aa` (since she has an affected son).

2. Genotype of Female B:
- Female B is unaffected (white circle).
- Since one parent is `aa` and the other is `Aa`, Female B must have inherited one `A` allele from her mother and one `a` allele from her father.
- Therefore, Female B’s genotype is `Aa`.

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Final Answers:

1. Is the albinism trait dominant or recessive?
- Recessive (explained above).

2. Genotypes for females A & B:
- Female A: Either `AA` or `Aa` (cannot be definitively determined without more information).
- Female B: `Aa`.

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Boxed Final Answer:

\[
\boxed{\text{Recessive, Female A: AA or Aa, Female B: Aa}}
\]