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Inherited Disorders and Birth Defects

Translocated Chromosomes

07/10/2007

Question:

My sister is 5 months pregnant. She just found out that she has a translocated chromosome. Hers is balanced. What is the chance that I will have a translocated chromosome? We have the same father and mother. Your help would be greatly appreciated!!

Answer:

If your sister inherited the balanced translocation from one of your parents, then you also could have inherited it. In theory, there is a 25% chance that the gametes (eggs or sperm) that the mom or dad produces – will have a normal chromosome complement, a 25% chance that the egg or sperm will have the balanced translocation and a 50% chance that the egg or sperm would produce an unbalanced chromosome complement. Usually the eggs or sperm that produce an unbalanced complement are miscarried or cause birth defects and other problems. So in your case, theoretically you have a 25% chance to be a carrier of a balanced chromosomal translocation - IF one of your parents has the translocation.

However, if the balanced translocation was not inherited, it occurred in your sister for the first time in your family, and then you would basically have no chance of having the translocation.

The only way to know if you are carrier of a balanced chromosomal translocation is to have your blood tested. Or, if your parents are tested, then you would know if your sister inherited it or if it happened for the first time in the family in her. Your sister of course can pass on the translocation, either balanced or unbalanced, to her children.

I would recommend that you talk to a geneticist or genetic counselor to discuss this. You can locate a genetics center near you at the National Society of Genetic Counselors' Resource center website below.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University