Reciprocal cross involves

Options

A. Cross between first fillial generation and recessive parent
B. Cross between first fillial generation and dominant parent
C. Selfing of first fillial generation
D. The same trait but carried by sexes opposite to those in the original or first cross

Answer

### Step-by-Step Text Solution:

1. **Understanding Reciprocal Cross**: A reciprocal cross is a genetic cross where two traits are examined, but the sexes of the parents are switched compared to the original cross. This means that if the first cross has a dominant trait in one sex, the reciprocal cross will have the dominant trait in the opposite sex.

2. **Identifying the Traits**: In a typical example, consider two plants: one tall (dominant trait) and one dwarf (recessive trait). In the first cross, we might have a tall female and a dwarf male.

3. **First Cross**:
- **Parents**: Tall plant (female) x Dwarf plant (male)
- **Gametes**: The tall female produces gametes with the dominant allele (T), while the dwarf male produces gametes with the recessive allele (t).
- **F1 Generation**: The offspring (F1 generation) will all be tall (Tt) since the tall allele is dominant.

4. **Reciprocal Cross**:
- Now, we switch the sexes of the parents for the reciprocal cross.
- **Parents**: Dwarf plant (female) x Tall plant (male)
- **Gametes**: The dwarf female produces gametes with the recessive allele (t), while the tall male produces gametes with the dominant allele (T).
- **F1 Generation**: The offspring (F1 generation) will again all be tall (Tt).

5. **Conclusion**: In both crosses, the trait being examined (height of the plants) is the same, but the sexes of the parents have been switched. Therefore, the correct definition of a reciprocal cross is that it involves the same trait but carried by sexes opposite to those in the original or first cross.

6. **Final Answer**: The answer is **D**: the same trait but carried by sexes opposite to those in the original or first cross.