Autosomal Dominant vs Autosomal Recessive: Reading the Pedigree
How to tell autosomal dominant from autosomal recessive inheritance on a pedigree chart — with the visual cues to look for in each generation.
- inheritance-patterns
- classroom
- autosomal
When a trait is caused by a single gene on a non-sex chromosome, it follows autosomal inheritance. The question is whether one copy of the allele is enough — dominant — or whether two copies are needed — recessive. The pedigree chart answers it at a glance, if you know what to look for.
Autosomal dominant: what to look for
- Every generation has affected people. The trait does not skip generations.
- Affected people have an affected parent. There are no “affected children of unaffected parents.”
- Both sexes affected roughly equally, and both sexes can transmit it.
- An affected person has about a 50% chance of passing it to each child, if the other parent is unaffected.
The classic giveaway is vertical transmission: the affected column runs down the chart like a pillar.
Autosomal recessive: what to look for
- Affected people can have unaffected parents. The parents are carriers — one copy each, no symptoms.
- Skipping generations. The trait may vanish for a generation, then reappear in siblings of carriers.
- Consanguinity is a hint. First-cousin unions increase the odds of both parents carrying the same recessive allele.
- Both sexes affected equally, and carriers are often drawn with a dot.
The classic giveaway is horizontal transmission: affected individuals cluster within a sibship — often two siblings out of four — with unaffected parents above.
The side-by-side checklist
| Cue | Dominant | Recessive |
|---|---|---|
| Affected in every generation? | Usually yes | Often skips |
| Affected child, unaffected parents? | No | Yes (both carriers) |
| Affected parent, unaffected child? | Yes (50% odds) | Yes |
| Carrier dots useful? | Rarely drawn | Standard |
| Consanguineous unions notable? | No | Yes |
Practice with real charts
The fastest way to internalize both patterns is to look at finished pedigrees:
- Autosomal dominant template — every generation shaded, vertical pattern visible immediately.
- Autosomal recessive template — unaffected carrier parents with affected children.
Open either in the maker, re-label the people with your own family or a classroom scenario, and you’ve made a practice chart in minutes. Teachers: both templates make excellent classroom exercises.