The risk of mongolism in a mother at the age 20 years is 1 : 000. what should be ratio when she is 45 yeas old :
**Core Concept**
The question is testing the understanding of the relationship between maternal age and the risk of Down syndrome (mongolism), a genetic disorder caused by an extra copy of chromosome 21. The risk of Down syndrome increases with maternal age, especially after the age of 35.
**Why the Correct Answer is Right**
The risk of Down syndrome is directly related to the age of the mother. The risk is 1 in 1,000 at the age of 20, but it increases significantly with age. By the age of 45, the risk is approximately 1 in 30. This is because the eggs in older women are more likely to have an extra copy of chromosome 21, which leads to Down syndrome. The risk is higher in older mothers due to the increased likelihood of meiotic errors during oogenesis.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not provide a logical increase in risk based on the maternal age.
* **Option B:** This option is incorrect because it suggests a decrease in risk, which is not consistent with the known relationship between maternal age and the risk of Down syndrome.
* **Option C:** This option is incorrect because it suggests a risk that is still relatively low, but not as high as the correct answer.
**Clinical Pearl / High-Yield Fact**
Remember that the risk of Down syndrome increases significantly with maternal age, especially after the age of 35. The risk is approximately 1 in 400 at the age of 40 and 1 in 30 at the age of 45.
**Correct Answer: C. 1 in 30.**