The sum of genotype and phenotype possible in the Fe generation of test cross if parents are TTRRDDEE and ttrrddee

Options

A. 16
B. 32
C. 27
D. 64

Answer

To solve the problem, we need to determine the sum of genotypes and phenotypes possible in the F2 generation from a test cross involving the parents TTRRDDEE and ttrrddee. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Genotypes of the Parents
- The first parent has the genotype TTRRDDEE (homozygous dominant for all traits).
- The second parent has the genotype ttrrddee (homozygous recessive for all traits).

### Step 2: Determine the F1 Generation
- When we perform a test cross between these two parents, the F1 generation will be heterozygous for all traits.
- Therefore, the genotype of the F1 generation will be TtRrDdEe.

### Step 3: Selfing the F1 Generation
- To find the F2 generation, we need to self-cross the F1 individuals (TtRrDdEe x TtRrDdEe).
- Each gene pair can be treated as a separate monohybrid cross.

### Step 4: Calculate the Phenotypic Ratio
- For each gene pair in a monohybrid cross, the phenotypic ratio is 3:1.
- Since there are 4 gene pairs (T, R, D, and E), we multiply the phenotypic ratio by the number of gene pairs.
- Thus, the phenotypic ratio for the F2 generation will be:
- Phenotypes: 3 (dominant) + 1 (recessive) for each gene pair = 3:1 for each gene.
- Total phenotypes: 4 pairs of genes give us 3^4 (dominant) and 1^4 (recessive) = 12 (dominant) + 4 (recessive) = 16.

### Step 5: Calculate the Genotypic Ratio
- For each gene pair in a monohybrid cross, the genotypic ratio is 1:2:1.
- Again, since there are 4 gene pairs, we multiply the genotypic ratio by the number of gene pairs.
- Thus, the genotypic ratio for the F2 generation will be:
- Genotypes: 1 (homozygous dominant) + 2 (heterozygous) + 1 (homozygous recessive) for each gene pair = 1:2:1 for each gene.
- Total genotypes: 4 pairs of genes give us 1^4 + 2^4 + 1^4 = 4 (homozygous dominant) + 8 (heterozygous) + 4 (homozygous recessive) = 16.

### Step 6: Calculate the Total Sum of Genotypes and Phenotypes
- Now, we add the total number of phenotypes and genotypes:
- Total phenotypes = 16
- Total genotypes = 16
- Total sum = 16 (phenotypes) + 16 (genotypes) = 32.

### Conclusion
The total sum of genotype and phenotype possible in the F2 generation of the test cross is **32**.

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