Read the following statements (i) to (iv)
(i) During transcription, adenine pairs with uracil.
(ii) The human genome has about 98% of junk DNA.
(iii) A human gene on an average contains 300 bps and there are about 30,000 genes in the human genome.
(iv) Y - chromosome of the human genome has the least number of genes , i.e., 321 in the human genome.
How may statements are CORRECT ?

Options

A. 5
B. 4
C. 3
D. 2

Answer

To determine how many statements are correct, let's analyze each statement step by step:

### Step 1: Analyze Statement (i)
**Statement:** During transcription, adenine pairs with uracil.

**Explanation:** In the process of transcription, DNA is used as a template to synthesize RNA. In RNA, adenine (A) pairs with uracil (U) instead of thymine (T), which is found in DNA. Therefore, this statement is **correct**.

### Step 2: Analyze Statement (ii)
**Statement:** The human genome has about 98% of junk DNA.

**Explanation:** The human genome is composed of approximately 98.5% non-coding DNA, often referred to as "junk DNA." This non-coding DNA includes various types of repetitive sequences and regulatory elements. Thus, this statement is also **correct**.

### Step 3: Analyze Statement (iii)
**Statement:** A human gene on average contains 300 bps and there are about 30,000 genes in the human genome.

**Explanation:** The human genome has been estimated to contain around 30,000 genes. While the average size of a gene can vary, it is often cited that many genes average around 300 base pairs (bps) in length. Therefore, this statement is **correct**.

### Step 4: Analyze Statement (iv)
**Statement:** Y-chromosome of the human genome has the least number of genes, i.e., 321 in the human genome.

**Explanation:** The Y chromosome is indeed known to have the least number of genes among human chromosomes. However, the actual number of genes on the Y chromosome is approximately 231, not 321 as stated. Therefore, this statement is **incorrect**.

### Conclusion
After analyzing all four statements:
- Statement (i): Correct
- Statement (ii): Correct
- Statement (iii): Correct
- Statement (iv): Incorrect

Thus, **3 statements are correct**.

### Final Answer
**3 statements are correct.**

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