A woman with a baby of downs syndrome comes for preconceptional counseling. Karyotype of the affected baby shows nondisjunction. What is the chance of downs syndrome in the subsequent Pregnancy?

**Core Concept**
The question is testing the understanding of the genetic mechanism underlying Down syndrome, specifically nondisjunction. Nondisjunction is a type of chromosomal error that occurs during cell division, resulting in an abnormal number of chromosomes. In the case of Down syndrome, it typically involves an extra copy of chromosome 21 (trisomy 21).

**Why the Correct Answer is Right**
Nondisjunction is a random event and does not have a familial pattern. Each pregnancy is an independent event, and the chance of nondisjunction occurring in a subsequent pregnancy is the same as in the first pregnancy. The risk of Down syndrome in a subsequent pregnancy is not influenced by the fact that the previous child had Down syndrome. The risk remains around 1 in 100 (1%) to 1 in 200 (0.5%) for women of average age, but it increases with maternal age.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the chance of Down syndrome in a subsequent pregnancy is not directly related to the previous child's condition. While there may be an increased risk with advanced maternal age, each pregnancy is an independent event.
* **Option B:** This option is incorrect because there is no established familial pattern for Down syndrome due to nondisjunction. The risk does not increase if there is a family history of the condition.
* **Option C:** This option is incorrect because the risk of Down syndrome is not significantly altered by the fact that the previous child had the condition. The risk remains around 1 in 100 (1%) to 1 in 200 (0.5%) for women of average age.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the risk of Down syndrome increases with maternal age, particularly after the age of 35. However, each pregnancy is an independent event, and the chance of nondisjunction occurring remains the same.

**Correct Answer:** D.