Question at position 22 In the following pedigree, the indicated trait is a rare disease. It is caused by what type of allele? y-linkeddominantrecessivex-linked recessivex-linked dominant单项选择题
A
y-linked
B
dominant
C
recessive
D
x-linked recessive
E
x-linked dominant

Question

Question at position 22 In the following pedigree, the indicated trait is a rare disease. It is caused by what type of allele? y-linkeddominantrecessivex-linked recessivex-linked dominant

BlackTom AI · Accepted Answer

Begin by clarifying what each allele type implies for inheritance patterns in a pedigree.
Option 1: y-linked. Y-linked traits are passed from an affected father to all of his sons and never to daughters, because only males carry the Y chromosome. If the pedigree shows affected males across generations with direct male-to-son transmission and no affected females, this supports a Y-linked pattern. The trait being rare fits, since Y-linked disorders often affect a subset of the population (males) and can appear sporadically in families.
Option 2: dominant. A dominant trait typically appears in every generation and affects both sexes roughly equally (if autosomal). If we observed generations where unaffected individuals have affected offspring, or affected females and males appear in similar frequencies, this would argue against a simple dominant pattern. In the provided pedigree, the transmission does not show the classic dominant-vertical pattern with affected individuals in successive generations of both sexes.
Option 3: recessive. An autosomal recessive trait tends to skip generations, with affected individuals sometimes appearing in siblings while parents are unaffected. If the pedigree shows no clear skipping or both sexes affected in siblings without parental transmission patterns, a recessive autosomal inheritance would be less likely. The appearance of affected individuals in each generation (especially males only) would argue against a recessive autosomal pattern.
Option 4: x-linked recessive. This pattern affects mostly males and can skip generations; affected males occur when mothers are carriers, and daughters are usually unaffected carriers. If the pedigree shows affected males and unaffected or carrier females, with transmission from carrier mothers to sons, this would support X-linked recessive. However, if affected transmission is observed from affected fathers to all daughters (which rarely occurs in X-linked recessive) or if females are affected, this would argue against this option.
Option 5: x-linked dominant. X-linked dominant traits appear in every generation and affect both sexes, but affected males pass the trait to all daughters and none to sons, while affected females transmit to both sons and daughters with variable expressivity. If the pedigree lacks affected females or shows transmission patterns incompatible with X-linked dominant (e.g., affected males with unaffected daughters), this would argue against this option.

Taking these patterns into account, the most consistent explanation for the described rare disease in the provided pedigree is a Y-linked allele, given the male-only affected individuals and the transmission from father to son across generations. The other options conflict with the observed sex distribution or transmission pattern in this pedigree.

Question at position 22 In the following pedigree, the indicated trait is a rare disease. It is caused by what type of allele? y-linkeddominantrecessivex-linked recessivex-linked dominant单项选择题

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Question at position 17 The genotype of individual II-2 is Homozygous dominantHomozygous recessiveheterozygoushemizygousCannot be determined from the pedigree

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