Question

Red-green color blindness is inherited as an X-linked recessive. How can a man with normal vision father a daughter who is red-green color blind?

Answer 1

Hint: Colour-blindness is a very common hereditary disease and is passed down from parents. The gene of red-green colorblindness is present on the X-chromosome. If the gene of colorblind is present then one out of three cone cells doesn’t develop or becomes less sensitive to light.

Complete answer:
-It is an X- linked recessive disease. The genes for colorblind must be present on both X chromosomes in females (XX) to present phenotypically. This means that the female will be colorblind if genes for colorblind are present on both X-chromosomes. If a woman has only one color-blind gene she is known as a ‘carrier’ but she won’t be colorblind.
-Males (XY) will be colorblind if the gene is present on only his single X chromosome. Therefore A color-blind boy can’t receive a color-blind gene from his father, even if his father is color blind because his father can only pass an X chromosome to his daughters.
-A daughter can become a carrier in one of two ways – she can acquire the gene from a carrier mother or from a colorblind father.
-This is the reason colorblindness is more common in males than in females.
-Sometimes father carries the gene of colorblind and is a carrier of the gene. For her daughter to become colorblind the mother must also be a carrier at least or should be colorblind. Then only her daughter will be colorblind.

Note: One must know that a colorblind father can not transmit the gene to his sons he can only transmit the colorblind gene to his daughter. While a mother can transmit the colorblind gene to her sons and daughter. Sons are not usually carriers because of the presence of only one X chromosome and also Y chromosome is smaller and therefore X chromosome expresses more phenotypically.