Which one of the following conditions correctly describes the sex determination mechanism ?

Options

A. Homozygous sex chromosomes (ZZ) determine female sex in birds
B. XO type of sex chromosomes determine male sex in grasshopper.
C. XXY condition in humans as found in Turner's syndrome, determines female sex .
D. Homozygous sex chromosomes (XX) produce male in Drosophila.

Answer

To solve the question regarding the correct description of the sex determination mechanism, we will analyze each option step by step.

### Step 1: Analyze Option A
**Statement:** Homozygous sex chromosome ZZ determines female sex in birds.

- In birds, the sex determination system is based on the ZW system.
- Males are ZZ (homozygous) and females are ZW (heterogametic).
- Therefore, this statement is incorrect because it incorrectly states that ZZ determines female sex.

**Hint:** Remember that in birds, the female is the heterogametic sex (ZW), while males are homozygous (ZZ).

### Step 2: Analyze Option B
**Statement:** X0 type of sex chromosome determines male sex in grasshopper.

- In grasshoppers, the sex determination system is X0.
- Females have two X chromosomes (XX), while males have one X chromosome (X0).
- Thus, the absence of a second sex chromosome in males (X0) does indeed determine male sex.
- This statement is correct.

**Hint:** Focus on the X0 system where the presence of one X chromosome in males leads to male determination.

### Step 3: Analyze Option C
**Statement:** XXY condition in humans as found in Turner syndrome determines female sex.

- The XXY condition is associated with Klinefelter syndrome, not Turner syndrome.
- Turner syndrome occurs in females with a missing X chromosome (X0).
- Klinefelter syndrome (XXY) results in male characteristics with some female traits.
- Therefore, this statement is incorrect.

**Hint:** Differentiate between Klinefelter syndrome (XXY) and Turner syndrome (X0) to understand their implications on sex determination.

### Step 4: Analyze Option D
**Statement:** Homozygous sex chromosome XX produces male in Drosophila.

- In Drosophila, the sex determination system is similar to humans.
- Females are XX and males are XY.
- Therefore, the statement that XX produces male is incorrect; XX produces female.

**Hint:** Recall that in Drosophila, XX is female and XY is male, which clarifies the sex determination mechanism.

### Conclusion
After analyzing all options, the only correct statement regarding sex determination is:

**Correct Answer:** B. X0 type of sex chromosome determines male sex in grasshopper.