Select the incorrect statement from the following.

Options

A. In birds, the chromosomes composition of the sperm determines
the sex of the progeny.
B. Cystic fibrosis is Mendelian disorder.
C. Increases in a whole set of chromosomes in an organism is known
as polyploidy.
D. Down's syndrome is chromosomal disorder and is due to trisomy of chromosome `21 ^(st)`.

Answer

To solve the question of selecting the incorrect statement from the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- **Statement:** "In birds, the chromosome composition of the sperm determines the sex of the progeny."
- **Analysis:** In birds, the sex determination system is different from that in mammals. Here, the female has ZW sex chromosomes, and the male has ZZ. The female gamete (egg) carries the Z or W chromosome, which determines the sex of the offspring. Therefore, this statement is **incorrect**.

2. **Analyze the Second Statement:**
- **Statement:** "Cystic fibrosis is a Mendelian disorder."
- **Analysis:** Cystic fibrosis is indeed an autosomal recessive disorder, which follows Mendelian inheritance patterns. Therefore, this statement is **correct**.

3. **Analyze the Third Statement:**
- **Statement:** "Increase in a whole set of chromosomes in an organism is known as polyploidy."
- **Analysis:** Polyploidy refers to the condition where an organism has more than two complete sets of chromosomes (e.g., 3n, 4n). This definition is accurate, making this statement **correct**.

4. **Analyze the Fourth Statement:**
- **Statement:** "Down syndrome is a chromosomal disorder and is due to trisomy of chromosome number 21."
- **Analysis:** Down syndrome is indeed caused by the presence of an extra chromosome 21, a condition known as trisomy 21. This statement is **correct**.

### Conclusion:
After analyzing all the statements, the first statement is the only incorrect one. Thus, the answer to the question is:

**Answer:** The incorrect statement is the first one: "In birds, the chromosome composition of the sperm determines the sex of the progeny."

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