QuestionSBA
QuestionChoice
Colour blindness is an x-linked recessive condition. As the father does not have colour blindness, this means that the boy has inherited the defective X-chromosome from the mother. A female inherits one X-chromosome from the mother and the father. The father has a normal X-chromosome, therefore she is unable to inherit the phenotype (she will be a carrier).
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a
0%
QuestionChoice
As the father is not affected, the mother carries the defective X-chromosome for colour blindness. There would only be a 100% chance that future daughters will be affected if both mother and father are colour-blind.
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d
100%
QuestionChoice
This would be true for an autosomal recessive inheritance pattern. However, colour blindness is an X-linked recessive condition requiring both X-chromosomes to be defective in a girl.
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b
25%
QuestionChoice
There is a 50% chance that the daughter will be a carrier of the condition. This is because there is a 50% chance she would inherit the defective X chromosome from the mother.
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c
50%
QuestionChoice
75% chance is not possible with an X-linked condition.
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e
75%
Concept
Chapter
2693
4475
X-linked recessive conditions
Topic
156
Medical Genetics
17699
A 4-year-old male patient is seen by an ophthalmologist and diagnosed with colour blindness, an X-linked recessive condition. His parents are unaffected. His parents would like his sister to be tested.

What is the likelihood that his little sister is colour-blind?
a