Colour blindness in humans is determined by a sex-linked gene - HSC - SSCE Biology - Question 19 - 2018 - Paper 1
Question 19
Colour blindness in humans is determined by a sex-linked gene. Two family trees are shown.
KEY
Normal vision male
Normal vision female
Colour-blind male
Colour-bli... show full transcript
Worked Solution & Example Answer:Colour blindness in humans is determined by a sex-linked gene - HSC - SSCE Biology - Question 19 - 2018 - Paper 1
Step 1
Determine the genotypes of individuals 1 and 2
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Answer
Individual 1 is a normal vision female and will have the genotype XX, while Individual 2 is a colour-blind male with the genotype XY. This means that he carries the allele for colour blindness on his X chromosome.
Step 2
Determine the potential genotypes of their offspring
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Answer
When these individuals have children, the possible combinations are:
Male offspring: XY (normal vision, inherits Y from father)
Female offspring: XX (normal vision, inherits X from mother). There is no potential for colour-blindness in males since they inherit their X from the colour-blind father (which is not possible in this case) and will inherit Y from the father.
Step 3
Calculate the probabilities for the offspring
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Based on the genotypes:
Male offspring: 0% colour-blind (as they will inherit Y from their father).
Female offspring: 0% colour-blind (as they will inherit X from their mother, which does not carry the colour-blind allele).
Step 4
Select the correct option from the table
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Answer
The correct row from the table is B: 0% male offspring are colour-blind and 0% female offspring are colour-blind.
