SOLUTION: SCB101 Punnett Square Practice Worksheet - Studypool - Free Printable

Problem Analysis and Solution

The task involves using Punnett Squares to determine the phenotypes and genotypes of possible puppies from two mating scenarios. Let's solve each part step by step.

---

#### Part 4: Both Dogs Have Black Fur

1. Given Information:
- The female dog has black fur, and her genotype is `ff` (homozygous recessive).
- The male dog also has black fur, and his genotype is `ff` (homozygous recessive).

2. Punnett Square Construction:
- The female contributes one allele (`f`) from each egg.
- The male contributes one allele (`f`) from each sperm.
- The Punnett Square will look like this:

```
| f | f |
-----------------
f | ff | ff |
-----------------
f | ff | ff |
```

3. Genotypes of Possible Puppies:
- All squares in the Punnett Square show `ff`.
- Therefore, all puppies will have the genotype `ff`.

4. Phenotypes of Possible Puppies:
- Since `ff` is the genotype for black fur, all puppies will have black fur.

5. Calculations:
- % of possible Genotypes:
- `FF`: 0% (no `F` alleles present)
- `Ff`: 0% (no `F` alleles present)
- `ff`: 100% (all squares are `ff`)
- % of possible Phenotypes:
- Black fur: 100% (all `ff` genotypes result in black fur)
- Grey fur: 0% (no `F` alleles present)

6. Final Answers for Part 4:
- `% of possible Genotypes:`
- `FF: 0%`
- `Ff: 0%`
- `ff: 100%`
- `% of possible Phenotypes:`
- Black fur: 100%
- Grey fur: 0%

---

#### Part 5: Both Dogs Are Heterozygous

1. Given Information:
- The female dog is heterozygous, so her genotype is `Ff`.
- The male dog is heterozygous, so his genotype is `Ff`.

2. Punnett Square Construction:
- The female contributes either `F` or `f` from each egg.
- The male contributes either `F` or `f` from each sperm.
- The Punnett Square will look like this:

```
| F | f |
-----------------
F | FF | Ff |
-----------------
f | Ff | ff |
```

3. Genotypes of Possible Puppies:
- The Punnett Square shows four possible genotypes:
- `FF` (top-left square)
- `Ff` (top-right and bottom-left squares)
- `ff` (bottom-right square)

4. Phenotypes of Possible Puppies:
- `FF` and `Ff` both result in black fur (dominant phenotype).
- `ff` results in grey fur (recessive phenotype).

5. Calculations:
- % of possible Genotypes:
- `FF`: 25% (1 out of 4 squares)
- `Ff`: 50% (2 out of 4 squares)
- `ff`: 25% (1 out of 4 squares)
- % of possible Phenotypes:
- Black fur: 75% (3 out of 4 squares: `FF` + `Ff`)
- Grey fur: 25% (1 out of 4 squares: `ff`)

6. Final Answers for Part 5:
- `% of possible Genotypes:`
- `FF: 25%`
- `Ff: 50%`
- `ff: 25%`
- `% of possible Phenotypes:`
- Black fur: 75%
- Grey fur: 25%

---

Final Answer:

- Part 4:
- `% of possible Genotypes:`
- `FF: 0%`
- `Ff: 0%`
- `ff: 100%`
- `% of possible Phenotypes:`
- Black fur: 100%
- Grey fur: 0%

- Part 5:
- `% of possible Genotypes:`
- `FF: 25%`
- `Ff: 50%`
- `ff: 25%`
- `% of possible Phenotypes:`
- Black fur: 75%
- Grey fur: 25%

Boxed Final Answer:
\[
\boxed{
\begin{array}{l}
\text{Part 4:} \\
\text{% of possible Genotypes:} \\
FF: 0\% \\
Ff: 0\% \\
ff: 100\% \\
\text{% of possible Phenotypes:} \\
\text{Black fur: } 100\% \\
\text{Grey fur: } 0\% \\
\\
\text{Part 5:} \\
\text{% of possible Genotypes:} \\
FF: 25\% \\
Ff: 50\% \\
ff: 25\% \\
\text{% of possible Phenotypes:} \\
\text{Black fur: } 75\% \\
\text{Grey fur: } 25\% \\
\end{array}
}
\]