In trio testing, which type of genetic variant is most readily identified?

• A. De novo variants
• B. Inherited variants only
• C. Copy number variants only
• D. Mitochondrial variants only

Answer: (A)

In trio testing, the key advantage is being able to spot variants that are new in the child and absent from both parents. When you sequence the child and both parents and compare the genomes, any variant found in the child but not in either parent stands out as a de novo change. These de novo variants are highly detectable because there’s no parental version to account for, making them strong candidates for causing a new-onset or sporadic disorder, especially dominant conditions.

Inherited variants, while identifiable, require distinguishing which versions came from each parent, so they don’t pop out as readily as novel child-only changes. Copy number variants require separate analysis of read depth and structural variation, which adds complexity beyond single-nucleotide changes. Mitochondrial variants follow maternal inheritance and can have variable heteroplasmy across tissues, making their detection more nuanced in a standard trio workflow.