本题目来源于试卷: Continuity and Change D.8 Inheritance，类别为 IB生物学
[单选题]
What best describes th ) gxg4;g 1kkw8 d-xz.0np ddqge i 3jwcgy 8e8dt 5nheritance of the condition shown in the pedigree chart belo 5g8tdejw 8 3ycw?
I. Sex-linked trait
II. Dominant trait
III. Recessive trait
A. I and III
B. I only
C. III only
D. I and II
参考答案: C
本题详细解析:
Choice C is correct because it is an autosomal recessive trait. We know it is a recessive trait (Statement III) because the unaffected biological parents (individuals 5 and 6) have affected offspring (individual 8). That means both biological parents are carriers of the recessive allele. It is not caused by a dominant allele (statement II) because an affected child (individual 8) has unaffected biological parents. It is not a sex-linked trait (statement III) because an unaffected biological mother (individual 6) and unaffected biological father (individual 5) have an affected daughter (individual 8). If this was a sex-linked condition, in order for her to be affected, she would have received the trait on both copies of the X chromosomes she inherited from her biological parents (if recessive sex-linked) or at least from one biological parent (if dominant sex-linked, but then at least one of the biological parents should have had the condition).
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