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The Sex-Linked Trait Calculator predicts the probability of X-linked recessive trait inheritance in offspring. X-linked traits follow distinctive inheritance patterns because males (XY) have only one X chromosome while females (XX) have two. This means males are hemizygous and express whatever allele they inherit from their mother.
Enter the mother's carrier status and the father's affected status to see the probabilities for sons and daughters separately.
For an X-linked recessive trait:
Sons inherit their X from their mother. If the mother is a carrier (X^A X^a), each son has a 50% chance of being affected. Sons inherit Y from their father, so the father's X-linked genotype does not affect sons.
Daughters inherit one X from each parent. A carrier mother × normal father can produce carrier daughters and normal daughters. An affected father always passes his X^a to daughters, making them at least carriers.
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A carrier mother and normal father: 50% of sons will be affected (e.g., color blind, hemophilia). 50% of daughters will be carriers, but none will be affected.
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When a carrier mother is crossed with an affected father, 50% of sons are affected. For daughters, 50% are carriers and 50% are affected (homozygous recessive).
Males have only one X chromosome (XY), so they express whatever allele is on that X. They cannot be carriers because they have no second X to compensate. Females have two X chromosomes, so a recessive allele on one X is usually masked by the normal allele on the other. This is why conditions like hemophilia and color blindness predominantly affect males.
Yes, but it is rare. A female must inherit the recessive allele from both parents (homozygous, X^a X^a). This requires an affected father and a carrier (or affected) mother. For rare conditions like hemophilia A (frequency about 1 in 5,000 males), affected females are extremely uncommon (about 1 in 25 million).
Common X-linked recessive conditions include red-green color blindness (affecting ~8% of males), hemophilia A and B, Duchenne muscular dystrophy, and glucose-6-phosphate dehydrogenase (G6PD) deficiency. X-linked dominant conditions also exist but are less common.
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