Solved Name Genetics Pedigree Worksheet A pedigree is a | Chegg.com - Free Printable

Let’s solve this step by step.

We’re looking at a pedigree chart. The key says:
- Open circle = female, unaffected
- Filled circle = female, affected
- Open square = male, unaffected
- Filled square = male, affected

Affected individuals are shown in black (filled shapes). Unaffected are white (open shapes).

We need to figure out genotypes for specific people and answer questions about whether the trait is dominant or recessive.

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First, let’s look at question 1:
Is this trait dominant or recessive? Explain your answer.

Look at generation II: Individuals II-3 and II-4 are both unaffected (white shapes), but they have children who ARE affected — III-3 (female, affected) and III-4 (male, affected).

That means two unaffected parents had affected kids. That can ONLY happen if the trait is recessive. Why? Because if it were dominant, at least one parent would have to show the trait to pass it on. But here, neither parent shows it — so they must be carriers (heterozygous) of a recessive allele.

So: Trait is recessive.

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Question 2:
How can you know for sure that individuals II-3 and II-4 are heterozygous?

Because they are unaffected (so they don’t show the trait), but they produced affected children (who must be homozygous recessive — meaning they got one recessive allele from each parent). So II-3 and II-4 must each carry one copy of the recessive allele — making them heterozygous.

If either was homozygous dominant, they couldn’t pass on a recessive allele. If either was homozygous recessive, they’d be affected — but they’re not. So only possibility: both are heterozygous.

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Now, identify genotypes:

We’ll use:
- “A” = dominant allele (normal/unaffected)
- “a” = recessive allele (causes disease/affected)

Since the trait is recessive, affected individuals = aa
Unaffected could be AA or Aa

Let’s go person by person:

I-1: Male, affected → must be aa

II-1: Female, unaffected. Her father (I-1) is aa, so he gave her an “a”. She’s unaffected, so she must have gotten an “A” from mom (I-2). So she’s Aa

III-3: Female, affected → must be aa

II-4: Female, unaffected. But she has affected children with II-3. As we said above, she must be Aa

Wait — the worksheet asks for:

> Try to identify the genotypes of the following individuals using the pedigree above.
(homozygous dominant, homozygous recessive, heterozygous)

Listed:
- III-3: ___
- II-1: ___
- I-1: ___
- II-4: ___

So:

- III-3: affected → homozygous recessive
- II-1: unaffected, but dad is affected → must be carrier → heterozygous
- I-1: affected → homozygous recessive
- II-4: unaffected, but has affected kids → must be carrier → heterozygous

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Question 3 is separate — it’s about eye color. Let’s do that too since it’s part of the worksheet.

Brown eyes (B) = dominant
Blue eyes (b) = recessive

Woman: brown-eyed, but her father had blue eyes → so her father was bb. She got one b from him. Since she has brown eyes, she must be Bb.

Man: brown-eyed, whose parents also had brown eyes. We don’t know his genotype yet — could be BB or Bb.

They have a son who is blue-eyed → bb.

That means the son got one b from mom and one b from dad.

Mom is Bb → can give b.

Dad must have given b → so dad must be Bb (not BB, because BB can’t give b).

So:

Grandparents (woman’s side):
- Mom’s dad: blue eyes → bb
- Mom’s mom: brown eyes → ? Could be BB or Bb — but since daughter is Bb, and got b from dad, mom could have given B or b. Not certain.

Actually, woman’s mother: brown eyes, married to bb man, had a brown-eyed daughter (Bb). So mom could be BB or Bb — we can’t tell for sure.

Similarly, man’s parents: both brown-eyed, but their son (the husband) is Bb. So each parent must have contributed at least one B, but since son is Bb, one parent gave B, other gave b? Wait no — son is Bb, so he got B from one parent and b from the other.

But both parents are brown-eyed → so they could be BB or Bb.

To produce a Bb child, possibilities:
- One parent BB, other Bb → possible
- Both Bb → possible
- One BB, other bb → but bb would be blue-eyed, but problem says both parents are brown-eyed → so not bb.

So man’s parents: both brown-eyed, produced a Bb son. So at least one parent must be Bb (to give the b allele). The other could be BB or Bb.

We cannot be certain of grandparents’ genotypes except:

Certain:
- Woman’s father: bb (blue eyes)
- Woman: Bb (brown eyes, but father was bb)
- Man: Bb (because he has blue-eyed son)
- Son: bb

Uncertain:
- Woman’s mother: could be BB or Bb
- Man’s parents: both brown-eyed; at least one is Bb, but we don’t know which or if both are.

Pedigree drawing isn’t something I can draw here, but I can describe:

Generation I (grandparents):

Left side (woman’s parents):
- Grandfather: blue eyes → filled square? No — wait, in standard pedigree, males are squares, females circles. Affected = filled.

But here, “affected” means blue eyes? Actually, in this context, blue eyes is the recessive trait — like the disease in first part.

So for eye color pedigree:

Use same symbols:
- Open = brown eyes (unaffected by blue-eye trait)
- Filled = blue eyes (affected)

Woman’s side:
- I-1 (her dad): blue eyes → filled square → bb
- I-2 (her mom): brown eyes → open circle → genotype unknown (BB or Bb)

Their child: II-1 (the woman) → brown eyes → open circle → Bb

Man’s side:
- I-3 (his dad): brown eyes → open square → genotype ? (must have given B or b to son)
- I-4 (his mom): brown eyes → open circle → genotype ?

Their child: II-2 (the man) → brown eyes → open square → Bb

Then II-1 and II-2 marry → have son III-1 → blue eyes → filled square → bb

In the pedigree, mark certain genotypes:

- I-1 (woman’s dad): bb → write “bb” under symbol
- II-1 (woman): Bb → write “Bb”
- II-2 (man): Bb → write “Bb”
- III-1 (son): bb → write “bb”

Others: uncertain — leave blank or write “B_” meaning could be BB or Bb.

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Now back to original pedigree questions.

Final answers for genotype identification:

- III-3: homozygous recessive
- II-1: heterozygous
- I-1: homozygous recessive
- II-4: heterozygous

Answers to questions:

1. Recessive — because two unaffected parents (II-3 and II-4) have affected children. Only possible if trait is recessive and parents are carriers.

2. They are unaffected but have affected children, so they must each carry one recessive allele — hence heterozygous.

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Final Answer:

Genotypes:
- III-3: homozygous recessive
- II-1: heterozygous
- I-1: homozygous recessive
- II-4: heterozygous

1. The trait is recessive. Two unaffected parents (II-3 and II-4) have affected children, which can only happen if the trait is recessive and both parents are carriers.

2. II-3 and II-4 are unaffected but have affected children. For a child to be affected (homozygous recessive), they must inherit one recessive allele from each parent. Since the parents are unaffected, they must each have one dominant and one recessive allele — making them heterozygous.

3. Pedigree description:
- Woman’s father: blue eyes (bb) — certain
- Woman: brown eyes (Bb) — certain
- Man: brown eyes (Bb) — certain (because he has blue-eyed son)
- Son: blue eyes (bb) — certain
- Woman’s mother: brown eyes — genotype uncertain (could be BB or Bb)
- Man’s parents: both brown eyes — at least one is Bb, but exact genotypes uncertain

Draw pedigree with four grandparents, two parents, one son. Mark certain genotypes as above.