Cystic fibrosis (autosomal recessive)

Scenario

The classic textbook pedigree for autosomal recessive inheritance — used in genetics courses, patient education, and clinical counseling to illustrate the 25% recurrence risk when both parents are carriers.

Annotation key

• carrier — half-filled symbol; one normal allele and one mutant allele (Aa)
• affected — fully filled symbol; two mutant alleles (aa)
• unaffected — open symbol; either homozygous normal (AA) or carrier (Aa) — cannot distinguish clinically without testing
• proband — triangle arrow; the first affected individual identified in the family

How to read

Both Generation I parents are carriers. Their Generation II children follow the expected 1:2:1 Mendelian ratio: one affected son (proband), one carrier daughter, one unaffected son. In Generation III, carrier daughter II-2 married a carrier II-4 — producing another affected granddaughter (III-1), reinforcing the recessive inheritance pattern.