Pedigree charts worksheet - Free Printable

Problem Analysis:

The worksheet focuses on understanding pedigrees and the inheritance of a recessive genetic trait, albinism, in humans. Albinism is caused by a recessive allele (`a`), while the dominant allele (`A`) results in a normal phenotype. The genotypes and their corresponding phenotypes are as follows:
- AA: Normal (homozygous dominant)
- Aa: Normal (heterozygous carrier)
- aa: Albino (homozygous recessive)

We will solve each part of the worksheet step by step.

---

Part 1: Genotypes and Phenotypes

#### Given Genotypes:
1. AA = Normal
- Both alleles are dominant (`A`), so the individual has a normal phenotype.

2. Aa = Normal
- One dominant allele (`A`) and one recessive allele (`a`). Since the dominant allele masks the recessive one, the individual has a normal phenotype but is a carrier of the albinism gene.

3. aa = Albino
- Both alleles are recessive (`a`), so the individual has the albino phenotype.

---

Part 2: Pedigree Analysis (First Pedigree)

#### Pedigree Description:
- Circles represent females.
- Squares represent males.
- Shaded symbols indicate individuals with the albino phenotype (`aa`).

#### Questions:
1. How many children does the couple have?
- The couple has 3 children (one circle and two squares).

2. What is the sex of the oldest child?
- The oldest child is a female (circle).

3. How many grandchildren does the couple have?
- The couple has 4 grandchildren (two circles and two squares).

---

Part 3: Pedigree Analysis (Second Pedigree)

#### Pedigree Description:
- Circles represent females.
- Squares represent males.
- Shaded symbols indicate individuals with the albino phenotype (`aa`).

#### Questions:
1. How many children did the original couple have?
- The original couple had 3 children (two circles and one square).

2. How many grandchildren do they have?
- The original couple has 5 grandchildren (three circles and two squares).

3. How many of their grandchildren are albino?
- There are 3 grandchildren who are albino (shaded symbols).

4. Create an extension to the pedigree to show the albino granddaughter marrying and having a son who is NOT albino.

- Step-by-Step Reasoning:
- The albino granddaughter has the genotype `aa` (since she is albino).
- To have a son who is NOT albino, the other parent must contribute at least one dominant allele (`A`).
- Therefore, the other parent must have a genotype of either `AA` or `Aa`.

- Extension of the Pedigree:
- Draw the albino granddaughter (`aa`) marrying someone with a genotype of `Aa` (carrier of albinism).
- Their offspring can have the following genotypes:
- `Aa` (normal, carrier)
- `aa` (albino)
- To satisfy the condition of having a son who is NOT albino, we choose the `Aa` genotype for the son.

- Final Extension:
- Add a new marriage line from the albino granddaughter (`aa`) to a partner with genotype `Aa`.
- Add a son with genotype `Aa` (normal, represented by an unshaded square).

---

Final Answers:

#### Part 1:
1. AA = Normal
2. Aa = Normal
3. aa = Albino

#### Part 2:
1. 3 children
2. Female
3. 4 grandchildren

#### Part 3:
1. 3 children
2. 5 grandchildren
3. 3 grandchildren are albino
4. Extension of the pedigree (see reasoning above).

---

Boxed Final Answer:

\[
\boxed{
\begin{array}{l}
\text{Part 1:} \\
\text{AA = Normal, Aa = Normal, aa = Albino} \\
\text{Part 2:} \\
\text{a) 3 children, b) Female, c) 4 grandchildren} \\
\text{Part 3:} \\
\text{a) 3 children, b) 5 grandchildren, c) 3 grandchildren are albino, d) See reasoning above.}
\end{array}
}
\]