If a person with Down syndrome marries a person without Down syndrome, is it possible for their child not to have Down syndrome?

I assume that there is a 50% chance that they could have a child that will not have down syndrome.

Is this correct?

It's very likely that a child with Down Syndrome did not inherit it. Less than 4% of people with this condition have inherited it. Check this article.

http://www.mayoclinic.com/health/down-syndrome/DS00182/DSECTION=causes

thanks so much for the article

You're very welcome.

No, your assumption is not correct. The chance of a child inheriting Down syndrome depends on the specific situation. Down syndrome is caused by the presence of an extra copy of chromosome 21. People with Down syndrome have 47 chromosomes instead of the usual 46.

If a person with Down syndrome marries a person without Down syndrome, the chances of their child inheriting Down syndrome will depend on whether the person with Down syndrome carries an extra copy of chromosome 21 in their reproductive cells (sperm or eggs).

Here's how you can determine the chances:

1. If the person with Down syndrome does not have an extra copy of chromosome 21 in their reproductive cells, there is a very low chance (almost negligible) that their child will have Down syndrome. The child will inherit the usual 46 chromosomes from the parent without Down syndrome.

2. However, if the person with Down syndrome does have an extra copy of chromosome 21 in their reproductive cells, there is a much higher chance that their child will have Down syndrome. The child will inherit the extra copy of chromosome 21, resulting in Down syndrome.

To accurately determine the probability, a genetic counselor or healthcare professional can perform specific tests and give you a more precise estimation based on the genetic makeup of the individuals involved.

It is important to note that while the chances of a child having Down syndrome can be discussed statistically, the uniqueness of each individual and their genetic makeup means that outcomes can vary.