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  4. A woman with one gene for haemophilia and one gene for colour blindness on one of the 'X' chromosomes marries a normal man. How will the progeny be?

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Q. A woman with one gene for haemophilia and one gene for colour blindness on one of the 'X' chromosomes marries a normal man. How will the progeny be?

Principles of Inheritance and Variation

Solution:

Haemophilia is a defect of blood which prevents its clotting. Colour blindness is the inability of certain human beings to distinguish red from green colour. Both these diseases are produced by a recessive gene which lies on the $X$-chromosomes. A woman having gene for haemophilia on one $X$-chromosome and gene for colourblindness on another $X$-chromosome will have genotype $X ^{ h } X ^{ c }$.
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Thus, progeny includes $50 \%$ daughters are carrier of haemophilia and $50 \%$ daughter are carrier of colourblindness whereas $50 \%$ sons are haemophiliac and $50 \%$ sons are colourblind.