Genetics pedigree problems | PPT - Free Printable

The image you've provided is a pedigree chart showing the inheritance of a trait across generations. Let's analyze and solve the problem step by step.

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🔍 Key Information from the Pedigree:

1. Symbols:
- Square = Male
- Circle = Female
- Red-filled symbol = Affected individual
- Unfilled = Unaffected

2. Given Notes:
- "Both males & females have trait = autosomal" → The trait is not sex-linked, so it's autosomal.
- "Child has trait but parents don't = recessive" → This indicates that the trait is recessive because an affected child can be born to two unaffected parents only if both are carriers (heterozygous).

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🧬 Step-by-Step Analysis:

#### Step 1: Determine Inheritance Pattern

We are told:
> "Child has trait but parents don't" → This is a classic sign of autosomal recessive inheritance.

In autosomal recessive traits:
- An individual must inherit two copies of the mutant allele (one from each parent) to be affected.
- Carriers (heterozygotes) are unaffected but can pass the allele to offspring.

Let’s look at the pedigree:

- In the bottom generation, there is a red square (affected male) whose parents are both unaffected (unfilled symbols).
- That means both parents must be carriers (heterozygous) — they have the gene but don’t show the trait.
- This confirms autosomal recessive inheritance.

Also, since both males and females are affected, it's not X-linked.

✔ So, the trait is autosomal recessive.

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#### Step 2: Assign Genotypes

Let’s use:
- A = dominant (normal)
- a = recessive (affected)

So:
- AA = normal (not carrier)
- Aa = normal carrier
- aa = affected

Now let’s assign genotypes:

##### First Generation (top):
- Left male: Unaffected → could be AA or Aa
- Left female: Affected → must be aa
- Right male: Unaffected → AA or Aa
- Right female: Unaffected → AA or Aa

But note: The affected male in the bottom row (red square) has unaffected parents.

So his parents must both be carriers (Aa).

Let’s trace that branch:

##### Second Generation (middle row):
- One couple produces an affected child (red square). Both parents are unaffected → both must be Aa.
- Therefore, this couple: Aa × Aa
- Offspring probabilities: 25% aa (affected), 50% Aa (carrier), 25% AA (normal)

This matches the pattern.

Now, look at the left side:
- The mother is affected (aa), father is unaffected (could be AA or Aa).
- Their children: some are unaffected, one is affected?
Wait — actually, in the left side:
- Affected mother (aa) × unaffected father (must be Aa or AA)
- But their children: all seem unaffected? Wait — let's check.

Actually, the affected individual (red square) in the bottom row is not a child of the affected woman on the top left.

Instead, the affected male is the child of two unaffected parents, as indicated by the arrow.

So focus on that couple in the middle row:
- Two unaffected individuals (circle and square) → produce an affected son (red square).
→ They must both be Aa.

Therefore, the trait is autosomal recessive.

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✔ Conclusion:

The trait shown in the pedigree is autosomal recessive.

#### Why?
- Affected individuals appear in generations where neither parent shows the trait → possible only if both are carriers.
- Both males and females are affected → not sex-linked.
- The pattern fits recessive inheritance.

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Final Answer:

The trait is inherited in an autosomal recessive manner.

This is supported by:
- Affected individuals having unaffected parents (indicating both parents are carriers),
- Equal occurrence in males and females,
- No skipping of generations (but with carrier parents, it can appear suddenly).

Let me know if you'd like a labeled version of the pedigree with genotypes!