Question

A normal woman whose mother was colorblind marries a hemophilic man. What are the chances of color blindness and hemophilia in their children?

Answer 1

Hemophilia

1. It is an inherited disorder where clotting after an injury does not occur properly leading to excessive bleeding.
2. The gene for clotting is located on the X chromosome and is recessive in nature.

Colorblindness

1. It is an inherited disorder where the person is unable to distinguish between certain colors.
2. The gene for colorblindness is located on the X chromosome and is recessive in nature.

X-linked disorders

1. If mutations present on one of the X chromosome is capable of developing the condition, it is called X-linked disorder.
2. Men are generally affected by this disorder as they have one copy of the X chromosome.
3. If women have one copy of the chromosome, they are carriers of the disease. If they have both the affected copies, they are affected by this disorder.
4. A colorblind woman with a normal man will produce 2 carrier females and 2 colorblind males.
5. When a carrier woman for colorblindness marries a hemophilic man, progeny with the below-mentioned phenotypes are produced-

Parents	XhY		XXC
Parent phenotype	Affected man (Hemophilic)		Carrier woman (colorblindness)
Gametes	Xh, Y		X, XC
Progeny	XXh	XCXh	XCY,	XY
Progeny phenotype	Carrier woman (hemophilia)	Carrier woman (hemophilia, colourblindness)	Affected male (colourblindness)	Normal male

6. Thus for colorblindness, 50% of sons will be affected and 50% normal; and 50% of daughters will be carriers and 50% normal.

7. For hemophilia, all daughters will be carriers and all sons will be normal.