Pedigree analysis of Hitchhiker's Thumb inheritance across four generations.

Let’s go step by step to solve the pedigree problem.

We’re told that “N” = normal thumb, and “n” = hitchhiker’s thumb (from the key on the right).

Looking at the pedigree:

- In generation IV, there are two shaded individuals (IV-2 and IV-4) — these have hitchhiker’s thumb.
- Their parents are III-1 and III-2 — both unshaded (normal thumbs).
- But they had children with hitchhiker’s thumb → that means the trait must be recessive. Why? Because if it were dominant, at least one parent would have to show the trait to pass it on. Since neither parent shows it but their kids do, the parents must be carriers (heterozygous), and the trait is recessive.

So for question 13: The trait is recessive.

Question 14: How do we know?
→ Because two unaffected parents (III-1 and III-2) produced affected children (IV-2 and IV-4). That only happens with recessive traits.

Question 15: How are III-1 and III-2 related?
→ They are married — husband and wife (as written in the answer space). Also, they are cousins? Wait — let’s look:
Actually, looking at the pedigree structure:
Generation II has three couples.
The middle couple in generation II (II-2 and II-3) have daughter III-2.
The left couple in generation II (II-1 and II-2?) — wait, actually, III-1 comes from the left branch, III-2 from the middle branch.
But in the diagram, III-1 and III-2 are connected as a mating pair — so they are spouses. The handwritten answer says “husband + wife”, which is correct.

Question 16: Name 2 individuals that have hitchhiker’s thumb.
→ Look for shaded symbols: IV-2 (male, shaded) and IV-4 (female, shaded). So: IV-2 and IV-4

Question 17: Name 2 individuals that were carriers of hitchhiker’s thumb.
→ Carriers are people who don’t show the trait (so unshaded) but carry the recessive allele (genotype Nn).
Who must be carriers?
Parents of affected children: III-1 and III-2 — because they are normal but had kids with hitchhiker’s thumb → they must both be carriers (Nn).
Also, maybe others? For example, II-2 and II-3? Let’s see:
III-2 is daughter of II-2 and II-3. III-2 is carrier (since she passed n to her kids). So II-2 and II-3 could be carriers or not — but we can’t be sure unless more info.
But definitely III-1 and III-2 are carriers.
Handwritten answer says “III-4 & III-5” — wait, that might be a mistake? Let’s check numbering.

Wait — let’s label the pedigree properly.

Generation I: I-1 (male), I-2 (female)

Generation II:
Left: II-1 (male), II-2 (female) — married
Middle: II-3 (male), II-4 (female) — married
Right: II-5 (male), II-6 (female) — married

Generation III:
From left couple: III-1 (male), III-2 (female) — wait no, actually:

Looking again:

In generation III:
Left side: III-1 (male) — son of II-1 and II-2? Actually, the lines connect:

Actually, standard pedigree reading:

I-1 and I-2 have three sons: II-1, II-3, II-5? Or maybe II-1, II-2, II-3? The diagram is a bit messy.

But based on connections:

III-1 and III-2 are the parents of IV-1, IV-2, IV-3, IV-4.

And III-1 is son of II-1 and II-2? And III-2 is daughter of II-3 and II-4?

Then III-1 and III-2 marry — so they are first cousins? But the question just asks how they are related — and the answer given is “husband + wife”, which is fine for this context.

Back to carriers: Who are definitely carriers?

- III-1 and III-2: yes, because they have affected children → must be Nn.

Also, since IV-2 and IV-4 are nn, they got one n from each parent.

Now, what about II-2 and II-3? If III-1 is Nn, and his parents are II-1 and II-2 (both normal), then at least one of them must be carrier. Similarly for III-2’s parents.

But the question asks to name 2 individuals that were carriers. The most obvious are III-1 and III-2.

But the handwritten answer says “III-4 & III-5” — let’s see where those are.

In generation III, on the right side: after the double line (which might indicate consanguinity?), there are III-4, III-5, III-6?

Actually, looking at the diagram:

After the middle couple in generation II (II-3 and II-4), they have daughter III-2.

Then there’s another couple: II-5 and II-6, who have three daughters: III-4, III-5, III-6? All unshaded.

But none of them have affected children shown, so we don’t know if they are carriers.

Whereas III-1 and III-2 definitely are.

Perhaps the handwritten answer meant III-1 and III-2? But it says “III-4 & III-5”.

Maybe typo? Or perhaps in some labeling...

To be safe, let’s stick with logic: carriers are heterozygotes who don’t show trait but can pass it.

Definite carriers: III-1 and III-2.

Also, since I-1 and I-2 are both normal, but they have grandchildren with hitchhiker’s thumb, they might be carriers too — but not necessarily; it could come from other branches.

But for sure, III-1 and III-2 are carriers.

Question 18: Write genotypes for each individual.

We’ll use N for normal (dominant), n for hitchhiker’s (recessive).

Start with affected individuals: they must be nn.

So:

IV-2: nn

IV-4: nn

Their parents: III-1 and III-2: both must be Nn (since they are normal but have nn children)

Now, III-1’s parents: II-1 and II-2 — both normal. III-1 is Nn, so he got n from one parent. So at least one of II-1 or II-2 is carrier. But we don’t know which, so we write N? for both? Or can we deduce?

Similarly, III-2’s parents: II-3 and II-4 — same thing.

But also, look at generation IV: IV-1 and IV-3 are normal. Their genotype could be NN or Nn. We don’t know for sure, so we write N?

Now, for the right side: II-5 and II-6 have three daughters: III-4, III-5, III-6 — all normal. No affected children, so we don’t know if they are carriers. So all get N?

But wait — in the diagram, under III-4, III-5, III-6, it says “N?” — so probably we leave as N? unless we can deduce.

Also, generation I: I-1 and I-2 — both normal. They have sons II-1, II-3, II-5? All normal. But since there are affected descendants, likely at least one of I-1 or I-2 is carrier. But again, not sure which, so N?

Now, specifically for the answers:

For question 17, if we must pick two carriers, best choices are III-1 and III-2.

But the handwritten answer says “III-4 & III-5” — perhaps in their labeling, III-4 and III-5 are the parents? No, in the diagram, III-4 and III-5 are sisters on the right, not parents of anyone shown.

Unless... oh! Wait a minute — in the diagram, there is a double line between III-2 and someone? Actually, looking closely:

In generation III, there is a person labeled "Nn" under III-2? And then connected to a male also labeled "Nn"? And they have children IV-1 to IV-4.

Actually, re-examining the image description:

It says: "III-2" is connected to a male (probably III-1) and they have four children: IV-1 (N?), IV-2 (nn), IV-3 (N?), IV-4 (nn)

And above them, in generation II, the parents of III-2 are II-3 and II-4, both labeled "N?"

Similarly, parents of III-1 are II-1 and II-2, both "N?"

On the right, II-5 and II-6 have three daughters: III-4, III-5, III-6, all "N?"

So for carriers, only III-1 and III-2 are confirmed carriers because they have affected children.

III-4, III-5, III-6 have no children shown, so we don't know if they are carriers.

Therefore, for question 17, the correct answer should be III-1 and III-2.

But the handwritten answer says "III-4 & III-5" — that might be an error.

Perhaps in some versions, the numbering is different.

To resolve, let's assume standard numbering.

Another thought: in the diagram, under the right branch, it says for III-4, III-5, III-6: "N?" but also, is there any indication they are carriers? No.

Whereas for III-1 and III-2, it explicitly says "Nn" in the diagram? Looking back at user's image description:

In the initial part, it says: "Nn" under III-2 and under the male she married (who is III-1?).

Yes! In the text: "Nn" is written below III-2 and below the male next to her (III-1).

So III-1 and III-2 are labeled as Nn — meaning carriers.

Whereas III-4, III-5, III-6 are labeled "N?" — unknown.

So for question 17, carriers are III-1 and III-2.

But the handwritten answer says "III-4 & III-5" — that must be a mistake.

Perhaps the student misread the numbers.

For accuracy, we'll go with III-1 and III-2.

Now for question 18: genotypes.

Let's list all individuals with known or deduced genotypes.

Generation I:
I-1: N? (normal, but may carry n)
I-2: N? (same)

Generation II:
II-1: N? (parent of III-1 who is Nn, so II-1 could be NN or Nn — unknown)
II-2: N? (same)
II-3: N? (parent of III-2 who is Nn)
II-4: N? (same)
II-5: N?
II-6: N?

Generation III:
III-1: Nn (carrier, as labeled and deduced)
III-2: Nn (same)
III-3: ? — wait, is there a III-3? In the left branch, after III-1 and III-2, there is III-3? The diagram shows: from II-1 and II-2, they have III-1 (male) and also another child? It says "III" with squares: one is III-1, then another square labeled "N?" — that might be III-3? But not connected to anyone.

Actually, in the diagram: under generation III, left side: two squares: one is III-1 (connected to III-2), and another square labeled "N?" — let's call him III-3.

Similarly, on the right, three circles: III-4, III-5, III-6.

So:

III-1: Nn
III-2: Nn
III-3: N? (no information)
III-4: N?
III-5: N?
III-6: N?

Generation IV:
IV-1: N? (normal child of III-1 and III-2; could be NN or Nn)
IV-2: nn (affected)
IV-3: N? (normal)
IV-4: nn (affected)

Now, for the answers to the questions:

13. recessive

14. Because two unaffected parents (III-1 and III-2) have affected children (IV-2 and IV-4). This is only possible if the trait is recessive.

15. Husband and wife (or spouses)

16. IV-2 and IV-4

17. III-1 and III-2 (carriers, as they are heterozygous)

18. Genotypes:

We need to write for each individual.

Since the diagram has labels, we can fill in:

I-1: N?
I-2: N?

II-1: N?
II-2: N?
II-3: N?
II-4: N?
II-5: N?
II-6: N?

III-1: Nn
III-2: Nn
III-3: N?
III-4: N?
III-5: N?
III-6: N?

IV-1: N?
IV-2: nn
IV-3: N?
IV-4: nn

Note: III-3 is the other son of II-1 and II-2, not married, no children, so genotype unknown.

Now, for the second part of the worksheet: "Determining Inheritance Patterns" with the pea color pedigree.

But the user didn't ask specific questions for that part — only up to 18 for the first pedigree.

The instruction was to solve the problem accurately, and the main task is questions 13-18.

So we'll focus on that.

Final Answers:

13. recessive

14. Two unaffected parents have affected children, which indicates the trait is recessive.

15. Husband and wife

16. IV-2 and IV-4

17. III-1 and III-2

18. Genotypes:

I-1: N?
I-2: N?

II-1: N?
II-2: N?
II-3: N?
II-4: N?
II-5: N?
II-6: N?

III-1: Nn
III-2: Nn
III-3: N?
III-4: N?
III-5: N?
III-6: N?

IV-1: N?
IV-2: nn
IV-3: N?
IV-4: nn

Note: The "?" means we cannot determine the second allele with the given information.

For question 17, even though the handwritten answer said III-4 and III-5, based on the pedigree logic, III-1 and III-2 are the definite carriers.

So we'll go with that.

Final Answer:
13. recessive
14. Two unaffected parents (III-1 and III-2) have affected children (IV-2 and IV-4), which only happens with recessive traits.
15. Husband and wife
16. IV-2 and IV-4
17. III-1 and III-2
18. Genotypes:
I-1: N?
I-2: N?
II-1: N?
II-2: N?
II-3: N?
II-4: N?
II-5: N?
II-6: N?
III-1: Nn
III-2: Nn
III-3: N?
III-4: N?
III-5: N?
III-6: N?
IV-1: N?
IV-2: nn
IV-3: N?
IV-4: nn