Which pattern of inheritance is characterised by needing only one copy of a pathogenic variant for an individual to be affected?

Question

BlackTom AI · Accepted Answer

When evaluating patterns of inheritance, it helps to map the statement to what each pattern requires in terms of allele copies.
Option 1: X-linked recessive. This pattern typically affects males more often and requires a pathogenic variant on the X chromosome. Females can be affected if they have two affected X chromosomes or certain skewed inactivation patterns, but the key feature is that males are often affected with only one mutated copy on their single X chromosome, not autosomes. Since the question specifies needing only one copy of a pathogenic variant to be affected and does not reference sex chromosomes, this option does not describe autosomal inheritance.
Option 2: Autosomal dominant. This pattern is defined by the need for only one pathogenic allele on a non-sex chromosome (an autosome) for the phenotype to manifest. Therefore, an affected individual has a 50% chance of passing the variant to each child, and one mutated copy is sufficient to cause disease. This aligns directly with the concept described in the question.
Option 3: Autosomal recessive. In this pattern, individuals must inherit two copies of the pathogenic variant (one from each parent) to be affected. Carriers with only one mutated allele are typically asymptomatic. Since the question emphasizes that a single copy is enough to cause disease, this option contradicts the defining feature of autosomal recessive inheritance.
Option 4: Y-linked. Y-linked conditions are passed from father to son and involve genes on the Y chromosome. Affected individuals are male, and the pattern requires a pathogenic variant on the Y chromosome. The statement about needing one copy does not capture the sex chromosome–restricted nature of Y-linked inheritance, and it does not fit the autosomal single-copy mechanism described in the question.
In summary, options describe different inheritance modes, but only autosomal dominant matches the description of disease occurring with a single pathogenic allele on an autosome, making it the pattern implied by the question. Each of the other options conflicts with either the chromosome type involved or the number of copies required for disease expression.

Which pattern of inheritance is characterised by needing only one copy of a pathogenic variant for an individual to be affected?

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