The genetic event that results in Klinefelter syndrome (XXY) is probably

Options

A. nondisjunction
B. deletion
C. parental imprinting
D. allosomal aneuploidy

Answer

**Step-by-Step Solution:**

1. **Understanding Klinefelter Syndrome**: Klinefelter syndrome is a genetic condition that occurs in males who have an extra X chromosome, resulting in the XXY chromosomal pattern.

2. **Identifying the Genetic Event**: The presence of an extra chromosome in Klinefelter syndrome is primarily due to a genetic event known as nondisjunction. Nondisjunction occurs when chromosomes fail to separate properly during cell division.

3. **Explaining Nondisjunction**: During the process of meiosis (specifically in anaphase), chromosomes should separate into different gametes. If this separation does not occur correctly, it results in gametes that have an abnormal number of chromosomes. When such a gamete fuses with a normal gamete during fertilization, it leads to an individual with an abnormal chromosome number.

4. **Linking Nondisjunction to Klinefelter Syndrome**: In the case of Klinefelter syndrome, the nondisjunction event leads to the formation of a sperm or egg cell that contains an extra X chromosome. When this gamete combines with a normal gamete (XY), the resulting zygote has an XXY configuration.

5. **Conclusion**: Therefore, the genetic event that results in Klinefelter syndrome (XXY) is nondisjunction, which leads to aneuploidy (an abnormal number of chromosomes).

**Final Answer**: The genetic event that results in Klinefelter syndrome (XXY) is probably nondisjunction.

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