Read following statements (1-4).
1. In transcriptoin, adenine pairs with uracil.
2. Regulation of lac operon by repressor is referred to as positive regulation.
3. The human genome has approximately 50,000 genes.
4. Haemophilia is a sex - linked recessive disease.
How many of the above statements are right ?

Options

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

Answer

To determine how many of the given statements are correct, we will analyze each statement one by one.

### Step 1: Analyze Statement 1
**Statement:** In transcription, adenine pairs with uracil.
**Analysis:** This statement is correct. During transcription, the DNA sequence is used to synthesize mRNA. In this process, adenine (A) in the DNA pairs with uracil (U) in the RNA. Therefore, this statement is true.

### Step 2: Analyze Statement 2
**Statement:** Regulation of lac operon by repressor is referred to as positive regulation.
**Analysis:** This statement is incorrect. The lac operon is regulated by a repressor protein that inhibits transcription when lactose is absent. This is an example of negative regulation, not positive regulation. Therefore, this statement is false.

### Step 3: Analyze Statement 3
**Statement:** The human genome has approximately 50,000 genes.
**Analysis:** This statement is also incorrect. The Human Genome Project estimated that the human genome contains about 20,500 genes, not 50,000. Therefore, this statement is false.

### Step 4: Analyze Statement 4
**Statement:** Haemophilia is a sex-linked recessive disease.
**Analysis:** This statement is correct. Haemophilia is indeed a sex-linked recessive disorder, primarily affecting males, as it is carried on the X chromosome. Therefore, this statement is true.

### Conclusion
Now, let's summarize the results:
- Statement 1: Correct
- Statement 2: Incorrect
- Statement 3: Incorrect
- Statement 4: Correct

**Total Correct Statements:** 2 (Statements 1 and 4)

### Final Answer
The number of correct statements is **2**.

---