Pedigree worksheet answers - Free Printable

Let's analyze each pedigree one by one to determine the inheritance pattern. In pedigree analysis, we use symbols:

- Squares = males
- Circles = females
- Shaded = affected individuals
- Unshaded = unaffected individuals

We'll look for patterns such as:
- Whether the trait appears in every generation (suggesting autosomal dominant)
- Whether it skips generations (suggesting autosomal recessive or X-linked recessive)
- Whether more males than females are affected (suggesting X-linked)
- Whether affected individuals have at least one affected parent (dominant) or not (recessive)

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1. First Pedigree

Pedigree I:
- Generation I: Male (1) is affected, female (2) is unaffected.
- Generation II: Children include both affected and unaffected individuals — 1 male (affected), 5 female (affected), 8 female (affected).
- Generation III: Affected individuals appear in offspring of affected parents.

Observations:
- Affected individuals appear in multiple generations.
- Both males and females are affected.
- Affected individuals have an affected parent (e.g., individual I-1 → II-1, II-5, II-8; II-5 → III-1, III-6, III-8).
- Unaffected individuals do not pass on the trait (e.g., II-2, II-3, II-4 are unaffected and have no affected children).

This suggests that the trait is passed from generation to generation and affects both sexes equally.

✔ Pattern: Autosomal Dominant

> Reasoning: The trait appears in every generation, affects both males and females, and affected individuals usually have at least one affected parent. This is classic autosomal dominant inheritance.

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2. Second Pedigree

Pedigree II:
- Generation I: Both parents are unaffected.
- Generation II: One daughter (II-2) is affected.
- Generation III: No affected individuals.

Observations:
- Affected individual (II-2) has two unaffected parents → this indicates the trait is not dominant (since dominant traits require at least one affected parent).
- The trait appears in a single generation and does not reappear in the next.
- Only one individual is affected in the family.
- It could be recessive, but since only one child is affected and the parents are unaffected, they must both be carriers.

However, no other descendants of the affected individual are affected (III-1 to III-9 are all unaffected), which may suggest sporadic mutation or incomplete penetrance, but given the data, it’s more likely autosomal recessive.

But wait: Only one child is affected, and the rest are unaffected. That fits autosomal recessive if both parents are carriers.

Also, no males vs. females show bias — both genders are equally represented.

✔ Pattern: Autosomal Recessive

> Reasoning: Affected individual has two unaffected parents (both must be carriers). Trait does not skip generations in a predictable way, but here it appears once in a generation with carrier parents. Since both sexes are affected and no sex bias, it’s autosomal recessive.

Note: If this were X-linked recessive, we would expect more males affected, and daughters of affected males would be carriers. But here, the affected individual is a female (II-2), and her father is unaffected — which is possible in recessive, but not typical for X-linked unless mother is carrier and father is normal.

But in X-linked recessive, a female needs two copies to be affected. So if father is unaffected, he cannot pass the allele. Therefore, if II-2 is affected and her father is normal, then the father cannot carry the allele. That makes X-linked recessive impossible.

So only possibility: Autosomal Recessive.

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3. Third Pedigree

Pedigree III:
- Generation I: Female (I-1) is affected, male (I-2) is unaffected.
- Generation II: Several affected individuals (II-1, II-4, II-8), mostly males.
- Generation III: More affected individuals, again mostly males.
- Generation IV: Males affected, females unaffected.

Observations:
- Affected individuals are mostly males.
- Affected males have unaffected daughters who can pass the trait.
- Affected males often have affected sons, but not necessarily.
- The trait does not skip generations — it appears in every generation.
- Affected females (like I-1) have affected sons (II-1, II-4, II-8).
- Unaffected males do not pass the trait.
- Females can be carriers (e.g., II-7, II-10, II-13 — unaffected but have affected sons).

This is classic X-linked recessive pattern.

> Key clues:
> - More males affected than females.
> - Affected males pass the trait to all daughters (who become carriers), but not to sons.
> - Carrier females can pass the trait to sons.
> - Affected females (rare) have affected fathers and carrier mothers.

In this case:
- I-1 is affected female → must have inherited the mutant allele from both parents.
- Her son II-1 is affected → inherited from mother.
- II-4 and II-8 are affected males → inherited from mother (I-1).
- Some daughters of affected males are unaffected (e.g., II-3, II-5, etc.), but some daughters are carriers (e.g., III-11, III-13).
- Affected males (e.g., II-1) have affected sons (III-1), indicating transmission through carrier daughters.

✔ Pattern: X-linked Recessive

> Reasoning: Males are predominantly affected, affected males pass the trait to daughters (who are carriers), and carrier females pass it to sons. This is characteristic of X-linked recessive inheritance.

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✔ Final Answers:

1. Autosomal Dominant
2. Autosomal Recessive
3. X-linked Recessive

Let me know if you'd like a diagram explanation or further clarification!