SOLUTION: Sicklecellanemiaonlinelab worksheet - Studypool - Free Printable

Let’s go step by step to solve this Punnett square problem about sickle cell disease.

We are told that both parents are carriers — meaning they are heterozygous for the sickle cell allele. That means each parent has one normal allele (S) and one sickle cell allele (s). So their genotype is Ss.

We need to draw a Punnett square to show what genotypes their children could have.

The Punnett square given in the image already shows:

```
| S | s
---------------------
S | SS | Ss
---------------------
s | Ss | ss
```

Wait — actually, looking at the image again, the student filled it out as:

Top row: S and s
Left column: s and s

So the squares are:
- Top-left: S from top + s from left → Ss
- Top-right: s from top + s from left → ss
- Bottom-left: S from top + s from left → Ss
- Bottom-right: s from top + s from left → ss

But that would mean both parents are ss? No — that can’t be right because the problem says both parents are heterozygous carriers, so they should both be Ss.

Actually, let me re-read the instructions:

> Suppose you have two carrier parents, both heterozygous for the sickle cell allele. Draw a Punnett square...

And then it says: “(The lowercase s has been underlined for you.)”

Looking at the grid provided:

It shows:

Top headers: S and s
Side headers: s and s

That suggests the student may have mislabeled the side — if both parents are heterozygous (Ss), then the side should also be S and s, not s and s.

But wait — maybe the student made a mistake? Let’s check the answers they wrote.

They answered:

a. 25% will suffer from sickle-cell anemia → which would be genotype ss

b. 50% will be carriers → genotype Ss

c. 25% will not carry the allele → genotype SS

That matches the correct Punnett square for two heterozygous parents (Ss x Ss):

Correct Punnett Square:

```
| S | s
---------------------
S | SS | Ss
---------------------
s | Ss | ss
```

So the four possible offspring genotypes are:
- SS → 1 out of 4 → 25% → unaffected, not carrier
- Ss → 2 out of 4 → 50% → carrier, no symptoms
- ss → 1 out of 4 → 25% → has sickle-cell anemia

Now let’s answer each question based on this correct setup.

---

Question a: What fraction of the children will suffer from sickle-cell anemia?

Only those with genotype ss will have the disease. That’s 1 out of 4 → 25%

Student wrote: “25% - There is one who is unaffected, one who is affected, and two who are carriers.” → This is correct in percentage, but the explanation mixes up terms. “Unaffected” usually means no disease — which includes both SS and Ss. But here they probably meant “not carrier” for SS. Still, the 25% is correct.

---

Question b: What fraction of the children will be carriers of sickle-cell anemia but show no symptoms?

Carriers are Ss — they have one copy of the sickle allele but don’t get sick. That’s 2 out of 4 → 50%

Student wrote: “50%” → Correct.

---

Question c: What fraction of the children will not carry the sickle-cell allele?

Not carrying the allele means they have no s allele at all → only SS genotype.

That’s 1 out of 4 → 25%

Student wrote: “25 were unaffected. 25 were affected. 50 were carries.” → They used numbers instead of fractions or percentages, and didn’t directly answer the question. The question asks for “fraction”, so we should say 25% or 1/4.

Also, note: “unaffected” might include carriers (since carriers don’t show symptoms), so saying “25 were unaffected” is misleading. Better to say: “25% have genotype SS — they do not carry the sickle-cell allele at all.”

---

So to summarize the correct answers:

a. 25% (or 1/4)
b. 50% (or 1/2)
c. 25% (or 1/4)

Even though the student’s Punnett square was drawn incorrectly (they put s and s on the side instead of S and s), their final answers match the correct ratios — probably because they knew the expected outcome.

But since the task is to solve accurately, we’ll give the correct reasoning and answers.

Final Answer:
a. 25%
b. 50%
c. 25%