Color vision deficiency
Color blindness in women
The most common kind of color blindness is the first type in which person cannot distinguish between red and green colors. This occurs in 8 percent of males and only 0.4 percent of females. This is an inherited disorder and affects men more commonly since the capacity for color vision is located on the X-chromosome. Women have two X-chromosomes, so the probability of inheriting at least one X with normal color vision is high. Men, on the other hand, have only one X chromosome. Women have two X chromosomes (XX), and men have an XY combination. If a woman is a carrier for color blindness, only one of her chromosomes will be affected, and for that reason, she will not be colorblind. Men, in contrast, only have one X chromosome, so whenever they carry the colorblindness gene, they will be colorblind.
Both X-chromosomes in women have to be affected in order for her to be colorblind. As a child inherits one chromosome from each parent, women will be colorblind only if both of her parents are color blind.
Color vision deficiency genetics
Color blindness is linked to mutations in X chromosome. There are two copies of a gene on the X-chromosome in females and males have only one copy of an X-linked gene. Many women are carriers of the genes but do not express the disorder. However, they pass the disorder to their sons, who may show signs of the disorder.
Since, the color blindness genetic functions from the X-linked mode of inheritance, it is possible to explain it in a very simple way, by examining the crisscross inheritance patterns.
- Father to male child – there are no chances to pass color blindness from a father to his male child, since male child gets only the Y chromosome from his father.
- Mother to male child – if mother carries the genetic material; male child may have as much as 50% of chances to inherit color vision deficiency because male child inherit the X-chromosome from their mothers.
- Father to female child – father cannot pass the disease to his female child. Female child will get one X-chromosome from her father but since the color vision deficiency is recessive, it is suppressed. However, daughters will pass off this trait to half of their children in future.
- Mother to daughter – daughter cannot inherit the disease from her mother, but there are 50 percent probability for a daughter to become a carrier of the disease.