Therory proposed by Bridges is

Options

A. Sex reversal by gene
B. Hormonal control of sex
C. Genic balance
D. Developlment of gynandromorph

Answer

**Step-by-Step Solution:**

1. **Identify the Theorist**: The theory proposed by Bridges is attributed to Calvin Bridges, a notable geneticist.

2. **Name the Theory**: The specific theory proposed by Calvin Bridges is known as the "Genic Balance Theory."

3. **Year of Proposal**: Calvin Bridges proposed the Genic Balance Theory in the year 1926.

4. **Understanding the Theory**: The Genic Balance Theory explains how sex is determined by the ratio of X chromosomes to autosomes in an organism.

5. **Sex Determination Mechanism**:
- In this theory, the sex of an organism is determined by the ratio of X chromosomes (X) to the number of sets of autosomes (A).
- The formula for determining sex can be summarized as:
- If the ratio (X/A) = 1, the organism is female (XX).
- If the ratio (X/A) = 0.5, the organism is male (XY).

6. **Application to Drosophila**: The Genic Balance Theory was first applied to the fruit fly, Drosophila melanogaster, where these ratios were observed to determine the sex of the flies.

7. **Conclusion**: The correct answer to the question regarding the theory proposed by Bridges is the "Genic Balance Theory."

---