Heterozygosity / dominance of phenotype can be determined by

Options

A. Back cross
B. Test cross
C. Reciprocal cross
D. Hybrid cross.

Answer

### Step-by-Step Solution:

1. **Understanding the Phenotypes**:
- In genetics, phenotypes are the observable traits of an organism. For example, in plants, we can have tall (dominant) and short (recessive) phenotypes.

2. **Identifying Genotypes**:
- The genotype refers to the genetic makeup of an organism. For the tall phenotype, the genotype could be either homozygous dominant (TT) or heterozygous (Tt). The short phenotype is represented by the homozygous recessive genotype (tt).

3. **Defining Heterozygosity and Dominance**:
- Heterozygosity means having two different alleles for a trait (e.g., Tt), while homozygosity means having two identical alleles (e.g., TT or tt). Dominance refers to the relationship between alleles, where the dominant allele (T) masks the effect of the recessive allele (t).

4. **Using a Test Cross**:
- To determine whether an individual with a dominant phenotype (tall plant) is homozygous (TT) or heterozygous (Tt), a test cross is performed. This involves crossing the individual in question with a homozygous recessive individual (tt).

5. **Analyzing the Results**:
- The offspring from the test cross will show different phenotypic ratios depending on the genotype of the tall plant:
- If the tall plant is homozygous (TT), all offspring will be tall (100% tall).
- If the tall plant is heterozygous (Tt), the offspring will show a 1:1 ratio of tall to short plants (50% tall and 50% short).

6. **Conclusion**:
- By analyzing the offspring from the test cross, one can determine whether the tall plant is homozygous or heterozygous. This method is a reliable way to assess the dominance of phenotype and heterozygosity.