Pedigree worksheet answers - Free Printable

Let's analyze each pedigree one by one to determine the inheritance pattern of the trait shown. In these diagrams:

- Blue squares (■) = affected males
- Blue circles (●) = affected females
- White squares/circles (□/○) = unaffected individuals

We'll examine each pedigree for clues about the inheritance pattern: Autosomal dominant, Autosomal recessive, X-linked dominant, or X-linked recessive.

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1. First Pedigree

```
I: ■ ○
1 2

II: ■ ○ □ ○ ● ○ □ ●
1 2 3 4 5 6 7 8

III: ● □ □ □ ○ ■ ○ ● ○
1 2 3 4 5 6 7 8 9
```

#### Observations:
- Affected individuals appear in every generation.
- Both males and females are affected.
- Affected parents can have unaffected children (e.g., I-1 is affected, but II-2, II-3, II-4 are not).
- Unaffected parents can have affected children (e.g., II-6 and II-7 are unaffected, but III-8 is affected).

But wait — let’s look more carefully.

- Individual I-1 (male) is affected.
- His daughter II-5 is affected.
- His son II-1 is affected.
- But his other children (II-2, II-3, II-4) are unaffected → suggests not all offspring are affected, so not fully penetrant? Or perhaps incomplete dominance?

Wait — II-5 is a female, and she is affected. Her mother I-2 is unaffected. So the trait must be passed from father to daughter — which is possible in autosomal dominant or X-linked.

But here’s a key point: I-1 is male and affected, and he has both affected and unaffected sons and daughters.

Now consider:
- II-1 (son of I-1) is affected → could be inherited.
- II-5 (daughter of I-1) is affected → also possible.
- But II-2, II-3, II-4 are unaffected → so not all children inherit it.

Also, II-8 (female) is affected, but her parents are II-6 (unaffected) and II-7 (unaffected) → both normal → yet they have an affected daughter.

This is critical: Two unaffected parents produce an affected child → this is only possible if the trait is recessive.

So, recessive inheritance is indicated because:
- Two unaffected parents (II-6 and II-7) have an affected child (III-8) → must be autosomal recessive.
- Also, I-1 is affected, but his wife I-2 is unaffected → their children include affected and unaffected → consistent with heterozygous carrier status.

But wait — I-1 is affected, so he must be homozygous or heterozygous depending on dominance.

But if it were dominant, then every child of an affected parent would have a 50% chance of being affected — but we see that some children are unaffected, which is fine.

However, two unaffected parents (II-6 and II-7) producing an affected child (III-8) is not possible in dominant inheritance unless there's new mutation, but that’s rare.

Therefore, this is autosomal recessive.

Let’s confirm:
- II-6 and II-7 are unaffected → both carriers (Aa)
- Their daughter III-8 is affected → aa → possible only in recessive
- I-1 is affected → aa
- I-2 is unaffected → Aa (carrier)
- Then children: AA, Aa, Aa, aa → matches observed: some affected, some not

Yes.

Also, III-6 is affected (male), parents II-4 and II-5 — II-4 is unaffected, II-5 is affected → if II-5 is aa, II-4 is Aa → child can be aa → yes.

So overall: Autosomal recessive

✔ Answer 1: Autosomal recessive

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2. Second Pedigree

```
I: □ ○
1 2

II: □ ● □ □ ○ ○ ○
1 2 3 4 5 6 7

III: ○ □ □ □ ○ ○ □ ○ □
1 2 3 4 5 6 7 8 9
```

#### Observations:
- Only one affected individual: II-2 (female)
- All others are unaffected
- II-2 has no affected children
- Her parents (I-1 and I-2) are unaffected
- She has siblings who are unaffected
- No other cases in family

This is unusual.

But wait — II-2 is affected, but her parents are unaffected → again, two unaffected parents have an affected child → must be recessive

But since only one person is affected, and no other family members show it, it could be a de novo mutation, but we’re to infer pattern.

Alternatively, could it be X-linked recessive?

But II-2 is a female, and she is affected. For X-linked recessive, a female needs two copies (X^a X^a) to be affected.

Her parents: I-1 (male) is unaffected → so he has X^A Y → so he gives X^A to daughters.

So daughter II-2 gets X^A from father → cannot be X^a X^a → so cannot be X-linked recessive.

Similarly, if it were X-linked dominant, then:
- Affected female (II-2) would pass to 50% of children
- But she has no affected children → possible if not expressed
- But her father is unaffected → so if it were X-linked dominant, she would need to get X^A from father → but father is unaffected → so he has X^a → so she would be X^a X^A → affected → possible

Wait — let’s try X-linked dominant.

In X-linked dominant:
- Affected father passes to all daughters, none of sons
- Affected mother passes to 50% of sons and daughters

Here:
- I-1 (father) is unaffected → so X^a Y
- I-2 (mother) is unaffected → X^a X^a
- Then II-2 (daughter) is affected → must be X^A X^a → but where did she get X^A?

She must have received it from one parent.

But father is X^a Y → gives X^a to daughter → so daughter gets X^a from father

Mother is X^a X^a → gives X^a → so daughter should be X^a X^a → unaffected

But she is affected → contradiction.

So no way she can be affected unless there’s a mutation.

But if we assume de novo mutation, then it could be any type.

But the question implies a clear pattern.

Alternatively, maybe it's autosomal recessive, and both parents are carriers.

Then II-2 is affected (aa), parents are Aa × Aa → 25% chance → possible.

And her children are all unaffected → possibly due to luck (small sample size) or incomplete penetrance.

But the problem is: only one person is affected, and no other cases.

But if it were dominant, then an affected individual would typically pass it to half their offspring — but II-2 has no affected kids → possible, but less likely.

But the key is: how did she get the allele?

If it’s autosomal recessive, then both parents are carriers → possible.

If it’s autosomal dominant, then she must have inherited it from one parent — but both parents are unaffected → so impossible unless new mutation.

Same for X-linked.

So the only way she can be affected with unaffected parents is autosomal recessive.

Thus, autosomal recessive is the most plausible.

Also, no males vs females preference, and only one case → could be rare recessive.

✔ Answer 2: Autosomal recessive

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3. Third Pedigree

```
I: ■ ○
1 2

II: □ ● □ ● ○ ○ ● □
1 2 3 4 5 6 7 8

III: ■ □ □ ○ ○ ■ ○ ○ ■ ○ ○ ■ ■ □ ○
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

IV: ○ □ ○ ● ● ○ □ ■ ■ □
1 2 3 4 5 6 7 8 9 10
```

#### Observations:
- Affected individuals in multiple generations
- More males than females affected?
- Let’s count:
- I: 1 male (1), 0 female → 1
- II: 2 females (2,4,7), 0 males → 3
- III: males: 1,6,9,12,13 → 5; females: 2,4,5,7,8,10,11,14,15 → 9 → actually more females
- IV: males: 8,9 → 2; females: 4,5 → 2 → equal

So not clearly sex-biased.

But look at I-1 (male) affected, his wife I-2 unaffected.

Their children:
- II-2 (female): affected
- II-4 (female): affected
- II-7 (female): affected
- II-1,3,5,6,8: unaffected

So all affected in generation II are females, and no males affected → interesting.

Now, II-2 (female affected) has children:
- III-1 (male): affected
- III-2 (male): unaffected
- III-3 (male): unaffected
- III-4 (female): unaffected
- III-5 (female): unaffected

So affected mother → son affected → possible in X-linked dominant or autosomal dominant

Similarly, II-4 (female affected) has:
- III-6 (male): affected
- III-7 (female): unaffected
- III-8 (female): unaffected

Again, affected female → son affected

Now, II-7 (female affected) has:
- III-12 (male): affected
- III-13 (male): affected
- III-14 (female): unaffected

So again, affected mother → sons affected

Now, III-1 (male affected) has:
- IV-4 (female): affected
- IV-5 (female): affected
- IV-1,2,3,6,7,10: unaffected

So affected male → daughters affected

Now, III-6 (male affected) has:
- IV-8 (male): affected
- IV-9 (male): affected

So affected male → sons affected

Now, III-12 (male affected) has:
- IV-8,9 → already counted

Wait — IV-8 and IV-9 are sons of III-12 → both affected

So affected males pass to sons → this suggests Y-linked?

But wait — females are also affected, like II-2, II-4, II-7, III-4, III-5, etc.

Females can't have Y chromosome → so not Y-linked

So what?

Look at I-1 (male affected) → his daughters (II-2, II-4, II-7) are affected → but his sons (II-1, II-3) are unaffected

So affected male → daughters affected, sons unaffected → classic X-linked dominant

Because:
- Male has X^A Y → passes X^A to all daughters, Y to sons
- Daughters get X^A → become affected
- Sons get Y → unaffected (unless mutation)

Then, affected females (like II-2) → genotype X^A X^a or X^A X^A → but since her mother is unaffected (I-2), she must be X^A X^a → carrier

Then she can pass X^A to sons or daughters → 50% chance

Indeed:
- II-2 → III-1 (son) affected → got X^A
- III-2 (son) unaffected → got X^a

Similarly, II-4 → III-6 (son) affected → got X^A

II-7 → III-12 (son) affected → got X^A

Now, affected males (like III-1) → he has X^A Y → passes X^A to daughters, Y to sons

So his daughters (IV-4, IV-5) are affected → yes

His sons (IV-1,2,3,6,7,10) → all unaffected → yes

Similarly, III-6 (male affected) → passes X^A to daughters, Y to sons → his sons (IV-8, IV-9) are affected? Wait — they are males, and they are affected.

But sons of an affected male get Y chromosome, not X → so they get X from mother

So if III-6 is affected (X^A Y), and his wife is unaffected (X^a X^a), then sons get X^a from mother → so should be unaffected → but IV-8 and IV-9 are affected → contradiction!

Wait — IV-8 and IV-9 are sons of III-6 and III-7 (who is unaffected) → so III-7 is X^a X^a → so sons get X^a → should be unaffected

But they are affected → so how?

Unless III-7 is carrier?

But III-7 is unaffected → so if it’s X-linked dominant, she must be X^a X^a → cannot be carrier

But if she is X^a X^a, then sons get X^a → should be unaffected

But IV-8 and IV-9 are affected → so they must have X^A → so must have gotten it from father → but father is III-6 → X^A Y → gives Y to sons → so sons get Y, not X → so cannot get X^A from father

Contradiction.

So cannot be X-linked dominant.

Wait — unless the trait is autosomal dominant?

Try that.

Assume autosomal dominant.

I-1 affected → genotype A_ (could be AA or Aa)

I-2 unaffected → aa

Children: Aa or aa → 50% chance affected

II-2, II-4, II-7 are affected → possible

Now, II-2 (Aa) × spouse (aa) → children: 50% affected

III-1 (son) affected → Aa → possible

III-2,3,4,5 unaffected → aa → possible

II-4 (Aa) × spouse → III-6 (son) affected → Aa → possible

II-7 (Aa) × spouse → III-12 (son) affected → Aa → possible

Now, III-1 (Aa) × spouse → IV-4, IV-5 affected → Aa → possible

III-6 (Aa) × spouse → IV-8, IV-9 affected → possible

But now, III-12 (Aa) → his wife is III-13? Wait, III-13 is male, unaffected → probably not spouse.

Looking at the diagram: III-12 is male, III-13 is male → no marriage shown between them.

Actually, III-12 has children: IV-8, IV-9 → so spouse is someone else.

But the spouse is not shown — assumed to be unaffected.

So if III-12 is Aa, and spouse is aa → then sons can be Aa → affected → yes

So possible.

But earlier we had issue with X-linked.

But now: can it be X-linked recessive?

Try that.

X-linked recessive:
- Affected males: X^a Y
- Affected females: X^a X^a

I-1 (male) affected → X^a Y

I-2 (female) unaffected → X^A X^A or X^A X^a

But she has affected daughters (II-2, II-4, II-7) → so daughters must be X^a X^a or X^a X^A

But to be affected, need X^a X^a

Daughter gets X^a from father → X^a (from father), and X^? from mother

To be affected, must get X^a from mother → so mother must be X^a X^a → but she is unaffected → impossible

So mother cannot be X^a X^a → so daughters get X^A from mother → so genotype X^A X^a → carrier, not affected

But II-2, II-4, II-7 are affected → so must be X^a X^a → impossible

So cannot be X-linked recessive

Back to autosomal dominant?

But earlier we saw that I-1 is affected, I-2 unaffected → children: II-2, II-4, II-7 affected → possible

But what about III-1 (male affected) → he has two affected daughters (IV-4, IV-5) → possible

But also, III-6 (male affected) → has two affected sons (IV-8, IV-9) → possible

But wait — III-6 is son of II-4 (affected) and II-5 (unaffected)

So if autosomal dominant, II-4 is Aa, II-5 is aa → III-6 is Aa → possible

Then III-6 × spouse (aa) → children: 50% Aa → IV-8 and IV-9 are both affected → possible (by chance)

Similarly, III-12 is son of II-7 (affected) and II-8 (unaffected) → so III-12 is Aa → then his sons IV-8, IV-9 → wait, IV-8 and IV-9 are sons of III-6 and III-7? Wait, names are confusing.

Looking at the diagram:

- III-6 is male → has children: IV-1,2,3,4,5,6 → so IV-4 and IV-5 are daughters of III-6

- III-12 is male → has children: IV-8, IV-9 → so IV-8 and IV-9 are sons of III-12

- III-13 is male → has children: IV-7,8,9,10 → wait, IV-8 and IV-9 appear twice? Probably typo.

Actually, looking closely:

IV: 1 2 3 4 5 6 7 8 9 10

- IV-1,2,3: children of III-1
- IV-4,5,6: children of III-6
- IV-7,8,9,10: children of III-13

But III-13 is male, unaffected → so if trait is dominant, he is aa → then children should be unaffected if spouse is aa

But IV-8 and IV-9 are affected → so must have Aa → so must have gotten A from parent

But III-13 is unaffected → aa → cannot give A → so spouse must be Aa → possible

So still possible.

But now — II-2 is female affected, her husband is II-3 (unaffected) → children: III-1 (affected), III-2,3,4,5 (unaffected) → so 1 out of 5 affected → possible for dominant

Similarly, II-4 × II-5 → III-6 (affected), III-7,8 (unaffected) → 1 out of 3 → possible

Now, is there any evidence against dominant?

No — all fits.

But wait — I-1 is affected, I-2 unaffected → children: II-1 (unaffected), II-2 (affected), II-3 (unaffected), II-4 (affected), II-5 (unaffected), II-6 (unaffected), II-7 (affected), II-8 (unaffected)

So 3 affected out of 8 → about 37.5% → close to 50% → possible

Now, is it possible that it's X-linked dominant?

Earlier we had a problem: III-6 (male affected) → his sons (IV-8, IV-9) are affected

But in X-linked dominant:
- Male (X^A Y) → gives Y to sons → sons get X from mother
- So sons get X^a from mother (if mother is X^a X^a) → so sons are X^a Y → unaffected
- But IV-8 and IV-9 are affected → so must be X^A Y → so must have gotten X^A from mother → so mother must be X^A X^a → but she is III-7 → unaffected → so cannot be X^A X^a → contradiction

So cannot be X-linked dominant

Similarly, X-linked recessive fails as before.

So only possibility left: Autosomal dominant

But wait — II-2 is female affected, her father is I-1 (affected), mother I-2 (unaffected) → so she is Aa

Her husband II-3 (unaffected) → aa

Children: III-1 (affected) → Aa → possible

But why are III-2,3,4,5 unaffected? → aa → possible

Similarly, II-4 (female affected) → Aa → her husband II-5 (unaffected) → aa → children: III-6 (affected) → Aa → possible

Now, III-12 (male affected) → Aa → his wife III-13 (unaffected) → aa → children: IV-8, IV-9 → both affected → possible (though unlikely, but possible)

But III-13 is male, and he is unaffected → so he is aa → then his children (IV-7,8,9,10) → must get a from him → so if affected, must get A from mother

But mother is III-12 → affected → Aa → so can give A → so IV-8, IV-9 can be Aa → affected → possible

But IV-8 and IV-9 are listed as sons of III-13 → so if III-13 is father, and he is aa, then sons get a from him → so to be affected, must get A from mother → mother is III-12 → affected → Aa → so yes, possible

But IV-8 and IV-9 appear in both III-6's and III-13's families? That can't be.

Looking back:

The diagram shows:

- III-6 has children: IV-1,2,3,4,5,6
- III-13 has children: IV-7,8,9,10

So IV-8 and IV-9 are sons of III-13, not III-6

So III-13 is father → unaffected → aa → so sons get a from him → so to be affected, must get A from mother → mother is III-12 → affected → Aa → so yes, possible

So no contradiction.

Thus, autosomal dominant fits.

But wait — I-1 is affected, and he has three affected daughters (II-2, II-4, II-7) and no affected sons → is that possible?

Yes — in autosomal dominant, sons and daughters have equal chance → so it's possible by chance that no sons are affected.

Similarly, II-2 has one affected son, others unaffected — possible.

So autosomal dominant is consistent.

But is there another clue?

Look at III-1 (male affected) → has two affected daughters (IV-4, IV-5) → possible

But III-6 (male affected) → has two affected daughters (IV-4, IV-5)? No — IV-4 and IV-5 are daughters of III-6 → yes

But IV-4 and IV-5 are affected → possible

But III-6 is male, and his wife is III-7 → unaffected → so she is aa → so daughters get a from mother → so to be affected, must get A from father → father is III-6 → Aa → so yes, can pass A

So possible.

Thus, all observations fit autosomal dominant inheritance

✔ Answer 3: Autosomal dominant

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✔ Final Answers:

1. Autosomal recessive
2. Autosomal recessive
3. Autosomal dominant

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Explanation Summary:

1. Pedigree 1: Affected individuals in multiple generations, but two unaffected parents have an affected child (II-6 and II-7 → III-8) → recessive. Males and females affected equally → autosomal recessive.

2. Pedigree 2: Only one affected individual (II-2), with unaffected parents → must be recessive (since dominant would require affected parent). No sex bias → autosomal recessive.

3. Pedigree 3: Affected in every generation, appears in both sexes, affected individuals have affected children, and no pattern of skipping generations → dominant. Equal sex distribution → autosomal dominant. (X-linked ruled out due to affected males having affected sons, which requires mother to carry, but mothers are often unaffected.)

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