The following pedigree shows the inheritance of an X-linked dominant trait in a family - VCE - SSCE Biology - Question 9 - 2010 - Paper 1
Question 9
The following pedigree shows the inheritance of an X-linked dominant trait in a family.
It is reasonable to assume that the
A. mother of II1 had the trait.
B. fathe... show full transcript
Worked Solution & Example Answer:The following pedigree shows the inheritance of an X-linked dominant trait in a family - VCE - SSCE Biology - Question 9 - 2010 - Paper 1
Step 1
A. mother of II1 had the trait.
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Answer
This option suggests that the mother of individual II1 expresses the trait. However, since II1 is a male, he inherits his X chromosome from his mother and a Y chromosome from his father. Therefore, if he has the trait, it is appropriate to consider the mother's genetic contribution.
Step 2
B. father of II1 had the trait.
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Answer
The father of II1 cannot pass on an X-linked trait to his son, as males inherit their Y chromosome from their father. Thus, this option cannot be correct.
Step 3
C. mother of II2 had the trait.
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Answer
This statement indicates that the mother of female II2 expresses the trait. Since the mother contributes one X chromosome and is affected, she must have the dominant trait. Therefore, this option is reasonable and true.
Step 4
D. father of II2 had the trait.
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Answer
Similar to option B, the father cannot pass on the X-linked trait to his daughter in this inheritance pattern. Therefore, this option is also incorrect.
