If we both have blue eyes, can our child have brown eyes?
Many decades ago, before eye color was understood, textbooks started teaching that blue eye color was ‘recessive to’ brown eye color. It was talked about as a simple fact. Turns out it isn’t that simple. First, eye color is determined by two separate layers in the iris (the colored part) of the eye. Just like you can change the color of a light by changing either the bulb or the lampshade, color depends on what is going on in both layers of the iris. Second, eye color is not genetically simple. It is decided by the interaction of more than one gene, so there is a big range of possibilities. Just as two short people can have a tall child, two persons with blue eyes can have a brown-eyed child.
Answer: Yes, it is possible for two blue-eyed parents to have a brown-eyed child.
Do genetic problems skip generations?
There is a difference between what the genes look like (the genotype) and what the person looks like (the phenotype). A genetic condition can appear to skip a generation two ways: 1) if someone is only mildly affected they might not know they have the condition, and 2) the abnormal genetics may be covered up by some other gene. The first concept is called variable expressivity – different people show disease to a different extent. The second is called non-penetrance – the abnormal genetics are there, but they aren’t showing up. There are some conditions, usually inherited on the X chromosome, which can affect mostly males and seem to ‘skip’ through the women.
Answer: No. If an abnormal gene “runs in the family”, it is present in every generation, but it may be too mild to cause problems, or may be inherited in such a way that the symptoms only show up in some people.
Can it be genetic if no one else in the family has it?
Sometimes a problem will be in the family for generations, but be so mild that no one is diagnosed. So it really is in the family but no one knows it. Sometimes a mutated gene can be hidden behind a working one and only shows up when both parents give an abnormal copy. Sometimes it is a new change in the genetics of the egg or sperm that become the baby.
The baby’s problem is because the parents blood doesn’t mix?
Only metaphorically, but not medically. Blood type is genetically determined, but genetic conditions in the baby aren’t about the parents’ blood. It is about the genetics in the eggs and the sperm. We talk about ‘blood relations’ as a way to talk about families, but the make up of the blood isn’t important in talking about the genetics of the baby (unless the baby has a genetic disease of the blood cells themselves). Also, blood type doesn’t tell us anything about genetic diseases.
Answer: No, it is the genetics of the egg and the sperm that matter.
Is baldness inherited from the mother?
Male pattern baldness is related to the androgen receptor gene, which is on the X chromosome. Men get their X chromosome from their mothers. Sooooo….
Answer: Yup, this one is true.
Angela Scheuerle provides genetic counseling in Dallas. She has a thriving pediatric practice and a busy life a high level of community focus.