USMLE purpose: Review genetics and pedigree-style probability questions using a clean inheritance-pattern workflow.

How to use this page

  1. Identify the inheritance pattern first.
  2. Determine carrier/affected status for each parent.
  3. Write the Punnett-style probability before choosing an answer.
  4. Use the toggles as rapid recall.

One-liner

Pedigree questions are probability questions: identify the inheritance pattern, assign parent genotypes, then multiply independent probabilities.

Inheritance recognition table

Pattern Classic clue Risk shortcut
Autosomal dominant Vertical transmission; affected parent often affected child Heterozygous affected parent → 50% affected children
Autosomal recessive Skipped generations; siblings affected Two carrier parents → 25% affected, 50% carrier
X-linked recessive Mostly males; no father-to-son transmission Carrier mother → 50% affected sons
Mitochondrial Maternal transmission Affected mother can transmit to all children

Anki-style rapid recall

Practice Question

Two unaffected parents have an affected child with an autosomal recessive disorder. What is the chance their next child is affected?