Bikini Bottom Genetics worksheet with SpongeBob and friends illustrating genetics problems.

Here is the complete solution to the “Bikini Bottom Genetics” worksheet, with explanations for each question.

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1. Heterozygous (He) or Homozygous (Ho)?

Definitions:
- Homozygous (Ho) = Two identical alleles (e.g., TT, tt, BB, bb)
- Heterozygous (He) = Two different alleles (e.g., Tt, Bb, Dd)

Answers:

| Genotype | He/Ho |
|----------|-------|
| TT | Ho |
| Bb | He |
| DD | Ho |
| Ff | He |
| tt | Ho |
| dd | Ho |
| Dd | He |
| ff | Ho |
| Tt | He |
| bb | Ho |
| BB | Ho |
| FF | Ho |

✔ Purebred genotypes (homozygous only):
TT, DD, tt, dd, ff, bb, BB, FF

✔ Hybrid genotypes (heterozygous only):
Bb, Ff, Dd, Tt

> *Note: “Purebred” means homozygous — same alleles. “Hybrid” means heterozygous — mixed alleles.*

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2. Phenotype for SpongeBob Genotypes

Given:
- Yellow body (Y) is dominant → blue (y) is recessive
- Square shape (S) is dominant → round (s) is recessive

Answers:

| Genotype | Phenotype |
|----------|-------------------|
| YY | Yellow body |
| Yy | Yellow body |
| yy | Blue body |
| SS | Square shape |
| Ss | Square shape |
| ss | Round shape |

> *Dominant trait appears if at least one dominant allele is present. Recessive trait only appears if both alleles are recessive.*

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3. Possible Genotypes for Patrick’s Phenotypes

Given:
- Tall head (T) is dominant → short (t) is recessive
- Pink body (P) is dominant → yellow (p) is recessive

Answers:

- Tall = TT or Tt
- Short = tt
- Pink body = PP or Pp
- Yellow body = pp

> *Dominant phenotype can be homozygous or heterozygous. Recessive phenotype must be homozygous.*

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4. SpongeBob & SpongeSusie’s Children (Shape)

Given:
- SpongeBob is heterozygous for square shape → genotype: Ss
- SpongeSusie is round → genotype: ss (recessive trait)

Punnett Square:

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

✔ A. Possible genotypes and phenotypes:
- Genotypes: Ss, ss
- Phenotypes: Square shape (Ss), Round shape (ss)

✔ B. Chances of square shape?
→ 2 out of 4 = 2/4 or 50%

✔ C. Chances of round shape?
→ 2 out of 4 = 2/4 or 50%

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5. Patrick & Patti’s Children (Body Color)

Given:
- Both are heterozygous for pink body → genotype: Pp

Punnett Square:

```
| P | p |
--------|--------|--------|
P | PP | Pp |
--------|--------|--------|
p | Pp | pp |
```

✔ A. Possible genotypes and phenotypes:
- Genotypes: PP, Pp, pp
- Phenotypes: Pink body (PP, Pp), Yellow body (pp)

✔ B. Chances of pink body?
→ 3 out of 4 = 3/4 or 75%

✔ C. Chances of yellow body?
→ 1 out of 4 = 1/4 or 25%

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6. Squidward & His Bride (Skin Color)

Given:
- Squidward’s family: light blue skin (dominant) → he is “purebred” → genotype: BB
- Bride: light green skin (recessive) → genotype: bb

Punnett Square:

```
| b | b |
--------|--------|--------|
B | Bb | Bb |
--------|--------|--------|
B | Bb | Bb |
```

✔ A. Possible genotypes and phenotypes:
- Genotype: All Bb
- Phenotype: All light blue skin (since B is dominant)

✔ B. Chances of light blue skin? → 100%

✔ C. Chances of light green skin? → 0%

✔ D. Would children still be purebreds?
→ No. Purebred means homozygous (BB or bb). All children are Bb — heterozygous → they are hybrids, not purebreds.

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7. Squidward’s Son & His Wife (Both Heterozygous)

Given:
- Son: heterozygous for light blue → Bb
- Wife: also heterozygous → Bb

Punnett Square:

```
| B | b |
--------|--------|--------|
B | BB | Bb |
--------|--------|--------|
b | Bb | bb |
```

✔ A. Possible genotypes and phenotypes:
- Genotypes: BB, Bb, bb
- Phenotypes: Light blue (BB, Bb), Light green (bb)

✔ B. Chances of light blue skin? → 3 out of 4 = 75%

✔ C. Chances of light green skin? → 1 out of 4 = 25%

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8. Mr. Krabs & Mrs. Krabs (Eyeballs)

Given:
- Mr. Krabs: homozygous tall eyeballs → TT
- Mrs. Krabs: heterozygous tall eyeballs → Tt
- Short eyeballs = recessive → tt

Punnett Square:

```
| T | t |
--------|--------|--------|
T | TT | Tt |
--------|--------|--------|
T | TT | Tt |
```

✔ A. Possible genotypes and phenotypes:
- Genotypes: TT, Tt
- Phenotypes: All tall eyeballs (since T is dominant; no tt possible)

✔ B. Did the hospital make a mistake?
→ Yes, probably.
Their child has short eyeballs (tt), which requires both parents to contribute a ‘t’ allele.
But Mr. Krabs is TT — he can only give a ‘T’. So it’s genetically impossible for them to have a child with short eyeballs.
Therefore, the baby cannot be theirs — likely a mix-up at the hospital.

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## ✔ Final Summary:

All questions answered with Punnett squares, genotype/phenotype logic, and clear explanations using Mendelian genetics principles. This worksheet reinforces understanding of dominance, recessiveness, homozygous/heterozygous, and probability in inheritance.

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