For the pedigree below , shaded symbols represent afflicted people. Males are squares; women are circles. If the trait is a sex-linkec I trait carried on the X chromosome, what is true about the mother represented by circle 1? She has one allele for the disorder. She has no alleles for the disorder. She has two alleles for the disorder. She has the genotype XXY.

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For the pedigree below , shaded symbols represent afflicted people. Males are squares; women are circles. If the trait is a sex-linkec I trait carried on the X chromosome, what is true about the mother represented by circle 1? She has one allele for the disorder. She has no alleles for the disorder. She has two alleles for the disorder. She has the genotype XXY.

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# Explanation In this problem, we are dealing with a sex-linked trait carried on the \( X \) chromosome. To determine the genotype of the mother represented by circle 1, we need to understand how sex-linked traits are inherited. 1. **Sex-Linked Traits on the \( X \) Chromosome:** - Males have one \( X \) chromosome and one \( Y \) chromosome (\( XY \)). - Females have two \( X \) chromosomes (\( XX \)). - A male inherits his \( X \) chromosome from his mother and his \( Y \) chromosome from his father. - A female inherits one \( X \) chromosome from each parent. 2. **Genotypes and Phenotypes:** - If a trait is recessive and carried on the \( X \) chromosome, a female must have two copies of the allele (one on each \( X \) chromosome) to express the trait. - A male only needs one copy of the allele on his single \( X \) chromosome to express the trait. 3. **Analyzing the Pedigree:** - Shaded symbols represent afflicted individuals. - Since males are squares and females are circles, we can identify the sex of each individual. Given that the trait is sex-linked and carried on the \( X \) chromosome, let's analyze the possible genotypes for the mother (circle 1): - If the mother (circle 1) is not shaded, she does not express the trait but can still be a carrier. - A carrier female has one normal allele and one allele for the disorder (\( X^N X^d \)). - If the mother had two alleles for the disorder (\( X^d X^d \)), she would be afflicted and shaded. - The genotype \( XXY \) is not applicable to females, as it represents a male with Klinefelter syndrome. Since the mother (circle 1) is not shaded but can pass the allele to her offspring, she must be a carrier. # Answer She has one allele for the disorder.

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