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The following points highlight the top five cases on colour blindness in humans.
Case # 1. Of what type will be the children with reference to colour blindness, when a man is colour-blind and his wife is normal?
Solution:
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The cause of the colour blindness is the presence of recessive (c) gene on the X chromosome.
Because man is colour-blind (Xc Y) and his wife is normal (XX), following will be the results while crossing:
Following will be the results after fertilization:
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(i) XXC, i.e., normal but carrier daughter.
(ii) XY, i.e., normal son.
Results:
No child will be colour-blind.
Case # 2. When a haemophilic male is mated with a heterozygous haemopbilic female, what haemophilic proportion will be resulted in each sex?
Solution:
Haemophilia is a disease that causes delayed clotting of blood. It is due to a recessive gene ‘h’, located on X chromosome.
Haemophilic gene is represented by ‘h’
Haemophilic male = XhY
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Heterozygous haemophilic female = XhX
Results:
One haemophilic daughter
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One carrier daughter
One haemophilic son
One normal son.
Case # 3. When a haemophilic male is mated with a homozygous non-haemophilic female-What will be the result?
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Solution:
Haemophilic male = XhY
Homozygous non-haemophilic female = XX
Result:
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A ratio of 2 (carrier daughter) and 2 (Normal son) will be produced.
Case # 4. Of what type will he the children with reference to colour blindness, when a woman is colour-blind and her husband is normal?
Solution:
Colour-blind woman = XCX
Normal man = XY
Result:
In such a case one normal and one colour-blind son, and one normal and one carrier daughter would be resulted.
Case # 5. When both the parents are colour-blind, can they produce a normal daughter?
Solution:
Results:
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The above results indicate that the colour-blind gene (c) is passed to both the X chromosomes of the daughter and so no normal daughter can be produced.
