A gene is said to be dominant, if

Options

A. It express it's effect only in homozygous stage.
B. It expressed only in heterozygous condition
C. It expressed both in homozygous and heterozygous condition.
D. It never expressed in any condition.

Answer

**Step-by-Step Solution:**

1. **Definition of Dominant Gene**: A gene is said to be dominant if it expresses its trait in the phenotype even when only one copy (allele) is present. This means that the dominant allele can mask the effect of a recessive allele.

2. **Alleles**: Genes exist in different forms called alleles. For example, in a trait where 'T' represents the dominant allele (tall) and 't' represents the recessive allele (short), the presence of at least one 'T' will result in a tall phenotype.

3. **Homozygous vs. Heterozygous**:
- **Homozygous Dominant**: When an organism has two identical dominant alleles (e.g., TT), it is homozygous dominant and will display the dominant trait.
- **Heterozygous**: When an organism has one dominant and one recessive allele (e.g., Tt), it is heterozygous and will also display the dominant trait due to the presence of the dominant allele.

4. **Recessive Trait**: A recessive trait (e.g., short, represented by 't') will only be expressed in the phenotype if the organism is homozygous recessive (tt). If there is a dominant allele present (T), the recessive trait will not be expressed.

5. **Gamete Formation**: During gamete formation, alleles segregate. For example, if a plant is heterozygous (Tt), it can produce gametes with either 'T' or 't'. If a plant is homozygous dominant (TT), it can only produce gametes with 'T'.

6. **Punnett Square Analysis**: To visualize inheritance patterns, a Punnett square can be used. For example, crossing a homozygous dominant (TT) with a heterozygous (Tt) will yield offspring that are either TT or Tt, all expressing the dominant trait.

7. **Conclusion**: Thus, a gene is dominant if it can express its trait in both homozygous (TT) and heterozygous (Tt) conditions, while the recessive trait only appears in the homozygous recessive condition (tt).

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