Colour blindness is inherited as an X-linked recessive condition - VCE - SSCE Biology - Question 5 - 2002 - Paper 1
Question 5
Colour blindness is inherited as an X-linked recessive condition.
It is reasonable to claim that a
A. colour-blind female must have a colour-blind father.
B. colour-... show full transcript
Worked Solution & Example Answer:Colour blindness is inherited as an X-linked recessive condition - VCE - SSCE Biology - Question 5 - 2002 - Paper 1
Step 1
A. colour-blind female must have a colour-blind father.
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Answer
This statement is true. Since color blindness is an X-linked recessive trait, a female (XX) must inherit one affected X chromosome from her father in order to express color blindness. As males (XY) only have one X chromosome, a color-blind father can only pass on his affected X chromosome to his daughters.
Step 2
B. colour-blind male must have a colour-blind mother.
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This statement is also true. A color-blind male inherits his X chromosome from his mother. Therefore, for him to be color-blind, his mother must have at least one affected X chromosome.
Step 3
C. colour-blind male must have a colour-blind grandfather.
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This statement is not necessarily true. A colour-blind male may have an unaffected paternal grandfather. The color blindness can skip a generation due to the inheritance pattern of X-linked traits.
Step 4
D. colour-blind female must have a colour-blind grandmother.
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This statement is also not necessarily true. A colour-blind female inherits her affected X chromosome from either her father, who must be color-blind, or her mother, who could be a carrier or color-blind. There is no direct requirement for her grandmother to be color-blind.
