Pedigree analysis worksheet - Free Printable

Problem Analysis:

The image provided is a pedigree chart, which is used in genetics to track the inheritance of traits within a family. The chart uses specific symbols to represent individuals and their relationships:

- Circles represent females.
- Squares represent males.
- Completely shaded symbols indicate that the individual has the trait.
- Half-shaded symbols indicate that the individual is a carrier of the trait.
- Unshaded symbols indicate that the individual neither has the trait nor is a carrier.

The task involves analyzing the pedigree chart to answer questions about the inheritance pattern of a particular trait.

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Step-by-Step Solution:

#### 1. Identify the Key Symbols:
- Ann (female): Unshaded circle → Does not have the trait and is not a carrier.
- John (male): Unshaded square → Does not have the trait and is not a carrier.
- All children of Ann and John are half-shaded (carriers), indicating they inherited one copy of the gene for the trait but do not express it.

#### 2. Analyze the First Generation (Children of Ann and John):
- Bert, Norris, Joan, Sue, Fred, David, Alice: All are half-shaded, meaning they are carriers of the trait but do not express it.

#### 3. Analyze the Second Generation (Grandchildren of Ann and John):
- Bert's children (Jenine and Frank):
- Jenine: Unshaded circle → Neither has the trait nor is a carrier.
- Frank: Half-shaded square → Carrier of the trait.
- Norris' children (Frank and Jill):
- Frank: Half-shaded square → Carrier of the trait.
- Jill: Unshaded circle → Neither has the trait nor is a carrier.
- Sue's children (George and Tom):
- George: Half-shaded square → Carrier of the trait.
- Tom: Half-shaded square → Carrier of the trait.
- Fred's children (none shown): No additional information.
- David and Alice's children (Louise, Janice, Marie):
- Louise: Unshaded circle → Neither has the trait nor is a carrier.
- Janice: Unshaded circle → Neither has the trait nor is a carrier.
- Marie: Unshaded circle → Neither has the trait nor is a carrier.

#### 4. Determine the Inheritance Pattern:
- Since all children of Ann and John are carriers but none of them express the trait, the trait is likely recessive.
- For a recessive trait:
- Both parents must be carriers to produce an affected offspring.
- Carriers (heterozygotes) do not express the trait but can pass it on to their offspring.

#### 5. Key Observations:
- None of the grandchildren express the trait, indicating that no homozygous recessive individuals are present.
- Some grandchildren (e.g., Frank, George, Tom) are carriers, suggesting that at least one parent in each case was a carrier.

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Final Answer:

Based on the analysis, the trait is recessive, and the carriers in the pedigree are:
- First generation (children of Ann and John): Bert, Norris, Joan, Sue, Fred, David, Alice.
- Second generation (grandchildren of Ann and John): Frank, George, Tom.

The unaffected individuals (neither carriers nor expressing the trait) are:
- Jenine, Jill, Louise, Janice, Marie.

Thus, the inheritance pattern is autosomal recessive.

$$
\boxed{\text{Autosomal Recessive}}
$$