Multiple Choice
Given a pedigree showing that Ryan is a male affected by an X-linked recessive disorder, which of the following is Ryan's genotype?
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2. Mendel's Laws of Inheritance
Pedigrees
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In a pedigree showing an autosomal recessive disorder, which of the following is most likely true about the parents of an affected individual?
A
Both parents are carriers of the recessive allele.
B
At least one parent must be affected by the disorder.
C
Only one parent needs to carry the recessive allele.
D
Both parents must be homozygous dominant.
Verified step by step guidance1
Understand that an autosomal recessive disorder requires an individual to inherit two copies of the recessive allele (one from each parent) to be affected.
Recognize that an affected individual has the genotype \( aa \), where \( a \) represents the recessive allele causing the disorder.
Since the affected individual has two recessive alleles, each parent must contribute one recessive allele, meaning both parents must at least be carriers with genotype \( Aa \).
Note that carriers (heterozygous \( Aa \)) do not show symptoms of the disorder but can pass the recessive allele to their offspring.
Conclude that both parents being carriers is the most likely scenario, while having one or both parents affected or homozygous dominant is inconsistent with the affected child's genotype.
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