The percentage proportion of homozygous parents in the `F_2` generation of a monohybrid cross is ……….the percentage proportion of homozygous parents in the `F_2` generation of a dihybrid cross

Options

A. is same as
B. is greater than
C. is lesser than
D. may be same greater but never lesser than

Answer

To solve the question regarding the percentage proportion of homozygous parents in the F2 generation of a monohybrid cross compared to a dihybrid cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Monohybrid Cross**:
- A monohybrid cross involves a single trait with two alleles. For example, consider the traits of plant height: tall (T) and short (t).
- When we cross two homozygous parents (TT and tt), the F1 generation will all be heterozygous (Tt) and exhibit the dominant phenotype (tall).

2. **F2 Generation of Monohybrid Cross**:
- When the F1 generation (Tt) is self-fertilized (Tt x Tt), we can use a Punnett square to determine the F2 generation.
- The genotypic ratio will be:
- TT (homozygous tall): 1
- Tt (heterozygous tall): 2
- tt (homozygous short): 1
- Therefore, the total ratio is 1 TT : 2 Tt : 1 tt, which means there are 2 homozygous individuals (TT and tt) out of 4 total individuals.
- The percentage of homozygous individuals in the F2 generation is \( \frac{2}{4} \times 100 = 50\% \).

3. **Understanding Dihybrid Cross**:
- A dihybrid cross involves two traits. For example, consider seed shape (Round - R, Wrinkled - r) and seed color (Yellow - Y, Green - y).
- We start with two homozygous parents (RRYY and rryy). The F1 generation will be all heterozygous (RrYy).

4. **F2 Generation of Dihybrid Cross**:
- When the F1 generation (RrYy) is self-fertilized (RrYy x RrYy), we can again use a Punnett square.
- The phenotypic ratio in the F2 generation will be 9:3:3:1, which indicates four different phenotypes.
- The genotypic combinations will include:
- Homozygous Round Yellow (RRYY): 1
- Homozygous Round Green (RRyy): 1
- Homozygous Wrinkled Yellow (rrYY): 1
- Homozygous Wrinkled Green (rryy): 1
- Heterozygous combinations (RrYy, Rryy, rrYy) will also be present.
- The total number of homozygous combinations is 4 out of 16 total combinations.
- The percentage of homozygous individuals in the F2 generation is \( \frac{4}{16} \times 100 = 25\% \).

5. **Comparison**:
- From the calculations:
- Monohybrid cross: 50% homozygous individuals in F2.
- Dihybrid cross: 25% homozygous individuals in F2.
- Therefore, the percentage proportion of homozygous parents in the F2 generation of a monohybrid cross is greater than that in a dihybrid cross.

### Conclusion:
The percentage proportion of homozygous parents in the F2 generation of a monohybrid cross is **greater than** the percentage proportion of homozygous parents in the F2 generation of a dihybrid cross.