Multiple Choice
Which X-linked recessive vision disorder, affecting about 8% of Caucasian males, is known as red-green?
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2. Mendel's Laws of Inheritance
Sex-Linked Genes
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In a pedigree showing inheritance of a sex-linked recessive trait, which of the following patterns is most likely to be observed?
A
Affected females are more common than affected males.
B
Affected males are more common than affected females.
C
Only females can be carriers of the trait.
D
Both males and females are equally likely to be affected.
Verified step by step guidance1
Understand that sex-linked recessive traits are typically located on the X chromosome, which means males (XY) and females (XX) have different probabilities of being affected.
Recall that males have only one X chromosome, so if they inherit the recessive allele on their single X chromosome, they will express the trait because there is no second X chromosome to mask it.
Recognize that females have two X chromosomes, so they must inherit two copies of the recessive allele (one from each parent) to express the trait, making affected females less common.
Note that females can be carriers if they have one recessive allele and one normal allele, meaning they do not express the trait but can pass it on to offspring.
Conclude that the most likely pattern observed in a pedigree for a sex-linked recessive trait is that affected males are more common than affected females, and only females can be carriers.
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