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"Is color-blindness hereditary?"
My husband was just turned down for admittance to medical technology repair school because he is color blind. The program trained technicians to repair x-ray, CT scan, and MRI machines as well as other medical equipment. He failed the wiring test because the wires were red and green and he could not distinguish between the two colors when they were not labeled with the letters. I understand how that could be a major problem in repairing expensive equipment that could save someone's life or not, but this has affected other areas of his life as well. His problem is that reds and greens both look brown to him. He also has trouble with traffic lights, and thank goodness they light up or he would not be able to drive. I understand that being color blind can be hereditary. Could this be passed on to our children?
Yes, color blindness is hereditary. There are two types of cells in the eye that sense light, called rod and cone cells. Cone cells sense color, and there are three different types of cone cells sense different colors of light. The most common forms of color blindness result from genetic abnormalities that affect the development or function of the type of cone cells that allow people to discriminate between the green-yellow-red spectrum of light. I recommend speaking with a medical geneticist to discuss this further. Although there have been over 50 different genes identified that can lead to color blindness, the most common genetic abnormalities responsible for red-green color blindness are found on one of the sex chromosomes called the X chromosome. Because of this, color blindness is commonly referred to as a sex-linked trait. Men have one X chromosome and one Y chromosome. Woman have two X chromosomes. All our other chromosomes exist in pairs, with no difference between males and females. Genetic abnormalities can be either dominant or recessive. If an abnormality is dominant, only one abnormal gene needs to be inherited in order to get a disease. For recessive abnormalities, every inherited copy of a gene has to be abnormal in order to get a disease. Color blindness is typically a recessive trait. Therefore, for a girl to get color blindness, both the X chromosomes she inherits (one from each parent) would have to have genes causing color blindness in order for her to be colorblind, making color blindness in females very uncommon. However, colorblindness in males is much more common because, by virtue of only having one X chromosome, all they have to do is inherit an X chromosome with a color blindness gene and they will be affected by color blindness. Because boys have to get their Y chromosome from their father (since only males have Y chromosomes to pass on) they get their only X chromosome from their mother (they get one of her X chromosomes at random), so boys inherit color blindness from their mother, who is typically not colorblind herself, but has inherited a color blindness gene from her colorblind father and carries it silently. This is the type of inheritance people tend to say "skips a generation". So, what does this mean for you. If you are not colorblind and your husband is, the answer to whether your kids are likely to be colorblind depends on the men on your side of the family. If your father or your maternal grandfather is colorblind, there is up to a 50% chance one of your children would be colorblind. If no males on the your side of the family have color blindness, then none of your children will be colorblind. However, to produce a girl, your husband has to pass on his X chromosome (rather than his Y, which would result in a boy), so all your daughters will carry the color blindness gene (without actually becoming color blind themselves) and their male children will have a 50% chance of being colorblind. All this information can be confusing. Fortunately there are two options to get more information. Any doctor will be able to give you general information about how color blindness is inherited, so you could make an appointment with a primary care physician. There is also a specialty of medicine called medical genetics, where physicians specialize in how genetic diseases affect people and are passed on to children. So you could also make an appointment with a medical geneticist to discuss how color blindness with be passed through future generations of your family.
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