In Down syndrome the chromosome number in each cell of body is

Options

A. 45
B. 47
C. 48
D. 49

Answer

**Step-by-Step Solution:**

1. **Understanding Down Syndrome**: Down syndrome, also known as Trisomy 21, is a genetic disorder caused by the presence of an extra copy of chromosome 21.

2. **Normal Chromosome Count**: In a typical human cell, there are 46 chromosomes, arranged in 23 pairs. Each parent contributes one chromosome to each pair.

3. **Cause of Down Syndrome**: In Down syndrome, there is a failure of the 21st chromosome to separate properly during the formation of sperm or egg cells. This phenomenon is known as non-disjunction.

4. **Chromosome Count in Gametes**: Due to non-disjunction, one gamete (sperm or egg) ends up with an extra chromosome, resulting in a total of 24 chromosomes in that gamete instead of the usual 23.

5. **Fertilization**: When this gamete with 24 chromosomes fuses with a normal gamete from the other parent (which has 23 chromosomes), the resulting zygote has 47 chromosomes in total (24 + 23 = 47).

6. **Conclusion**: Therefore, in individuals with Down syndrome, the chromosome number in each cell of the body is 47.

**Final Answer**: In Down syndrome, the chromosome number in each cell of the body is **47**.

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