Read statements `a-d`.
(a) In transcription, adenosine pairs with uracil
(b) Regulation of lac operon by repressor is positive regulation
(c) Human genome has approximate 50,000 genes
(d) Haemophilia is sex-linked recessive disease
How many of above statement are correct ?

Options

A. Four
B. One
C. Two
D. Three

Answer

To determine how many of the statements (a-d) are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement (a)**: "In transcription, adenosine pairs with uracil."
- In transcription, adenine (a nitrogenous base) pairs with uracil (another nitrogenous base) in RNA. However, the statement incorrectly uses "adenosine," which is a nucleoside (adenine + sugar). Thus, this statement is **incorrect**.

2. **Statement (b)**: "Regulation of lac operon by repressor is positive regulation."
- The lac operon is regulated by a repressor protein, which inhibits transcription when lactose is not present. This is an example of **negative regulation**. Therefore, this statement is also **incorrect**.

3. **Statement (c)**: "Human genome has approximately 50,000 genes."
- Current research indicates that the human genome contains approximately **20,500 genes**, not 50,000. Thus, this statement is **incorrect**.

4. **Statement (d)**: "Haemophilia is a sex-linked recessive disease."
- Haemophilia is indeed a genetic disorder that is **sex-linked and recessive**. It is caused by mutations in genes located on the X chromosome. Therefore, this statement is **correct**.

### Conclusion:
After analyzing all four statements:
- Statement (a): Incorrect
- Statement (b): Incorrect
- Statement (c): Incorrect
- Statement (d): Correct

Thus, **only one statement (d) is correct**.

### Final Answer:
**1 statement is correct.**