In a cross between negro and albino skin colour of humans showing polygenic inheritance, the phenotypic ratio in `F_(2)` generation will be

Options

A. `9:3:3:1`
B. `1:6:15:20:15:6:1`
C. `1:4:6:4:1`
D. `1:2:2:4:1:2:1:2:1`

Answer

To solve the problem regarding the phenotypic ratio in the F2 generation from a cross between Negro and Albino skin color in humans, which shows polygenic inheritance, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Polygenic Inheritance**:
- Skin color in humans is determined by multiple genes (specifically three genes in this case). Each gene can have multiple alleles contributing to the overall phenotype.

2. **Identify the Parental Genotypes**:
- Let's assume that the Negro skin color is represented by the dominant alleles (A, B, C) and the Albino skin color is represented by the recessive alleles (a, b, c).
- Thus, the Negro parent can be represented as AABBCC and the Albino parent as aabbcc.

3. **Determine the F1 Generation**:
- When we cross AABBCC (Negro) with aabbcc (Albino), all F1 offspring will have the genotype AaBbCc.
- The F1 generation will exhibit an intermediate phenotype, which is a blend of both parental traits.

4. **Selfing the F1 Generation**:
- To find the F2 generation, we need to self-cross the F1 individuals (AaBbCc x AaBbCc).
- This will involve using a Punnett square to determine the possible combinations of alleles in the offspring.

5. **Calculate the Phenotypic Ratios**:
- The F2 generation will display a range of phenotypes due to the combination of alleles from the F1 generation.
- The expected phenotypic ratio for polygenic inheritance in this case is 1 (extreme Negro): 6 (moderately dark): 15 (medium): 20 (intermediate): 15 (light): 6 (moderately light): 1 (extreme Albino).

6. **Verify the Total**:
- Adding the numbers from the phenotypic ratio: 1 + 6 + 15 + 20 + 15 + 6 + 1 = 64, which corresponds to the total number of phenotypes expected in the F2 generation.

7. **Conclusion**:
- Therefore, the phenotypic ratio in the F2 generation from the cross between Negro and Albino skin color humans, showing polygenic inheritance, will be 1:6:15:20:15:6:1.

### Final Answer:
The phenotypic ratio in the F2 generation will be **1:6:15:20:15:6:1**.

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