Find out the `F_(2)` phenotypic ratio, when a mulatto individual is cross ed to its homozygous dominant individual. (Given that skin colour is controlled by three gene pairs )

Options

A. `1:4:6:4:1`
B. `1:1:1:1`
C. `1:3:3:1`
D. `3:1`

Answer

To solve the problem of finding the F2 phenotypic ratio when a mulatto individual is crossed with a homozygous dominant individual, we will follow these steps:

### Step 1: Understand the Genotypes
- **Homozygous Dominant Individual**: This individual has the genotype AABBCC (all alleles are dominant).
- **Mulatto Individual**: This individual is heterozygous for all three genes, so its genotype is AaBbCc.

### Step 2: Determine Gametes
- The homozygous dominant individual can only produce one type of gamete: ABC.
- The mulatto individual can produce the following gametes: ABC, AbC, ABc, abC, aBc, Abc, ABc, abc (total of 8 combinations).

### Step 3: Cross the Gametes
Using a Punnett square, we can cross the gametes from both parents. Since the homozygous dominant parent can only produce one type of gamete (ABC), the offspring will inherit one allele from the homozygous dominant and one from the mulatto individual.

### Step 4: Determine the Offspring Genotypes
The possible combinations from the cross (homozygous dominant ABC with the gametes from the mulatto AaBbCc) will yield the following genotypes:
1. AABBCC (darkest skin)
2. AABBCc (dark skin)
3. AABbCC (dark skin)
4. AABbcc (medium dark skin)
5. AaBBCC (dark skin)
6. AaBBCc (medium dark skin)
7. AaBbCC (medium dark skin)
8. AaBbCc (medium skin)

### Step 5: Identify the Phenotypes
From the combinations above, we can categorize the phenotypes based on the dominance of the alleles:
- Darkest Skin: AABBCC (1)
- Dark Skin: AABBCc, AABbCC, AaBBCC (3)
- Medium Dark Skin: AABbcc, AaBBCc, AaBbCC (3)
- Medium Skin: AaBbCc (1)

### Step 6: Calculate the Phenotypic Ratio
The phenotypic ratio based on the combinations is:
- Darkest Skin: 1
- Dark Skin: 3
- Medium Dark Skin: 3
- Medium Skin: 1

Thus, the F2 phenotypic ratio is **1:3:3:1**.

### Final Answer
The F2 phenotypic ratio when a mulatto individual is crossed with a homozygous dominant individual is **1:3:3:1**.

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