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 one by one:

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

**Analysis:**
- In DNA, adenine (A) pairs with thymine (T). However, during transcription, when RNA is synthesized from the DNA template, adenine pairs with uracil (U) instead of thymine.
- Therefore, this statement is **correct**.

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

**Analysis:**
- The Human Genome Project revealed that only about 1-2% of the human genome consists of coding DNA (genes), while the remaining approximately 98% does not code for proteins and is often referred to as "junk DNA."
- Hence, this statement is **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.

**Analysis:**
- The Human Genome Project estimated that the human genome contains approximately 30,000 genes. The average length of a gene can vary, but it is reasonable to say that many genes have an average length around 300 base pairs (bps).
- Therefore, this statement is also **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.

**Analysis:**
- The Y chromosome is known to have the least number of genes compared to other chromosomes. However, the commonly accepted number of genes on the Y chromosome is approximately 231, not 321.
- 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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