In genetics, a pedigree chart is a family tree that tracks one trait or condition: who has it, who carries it, and how it passed from parents to children. Biology classes use pedigrees to work out how a trait is inherited, and genetic counselors use them to estimate risk for a family.
Pedigree symbols
| Symbol | Meaning |
|---|---|
| Male (square). | |
| Female (circle). | |
| Sex unknown (diamond). | |
| Affected: the symbol is filled in. | |
| Carrier (heterozygous, not affected): half filled. Used mostly for autosomal recessive traits. | |
| Carrier, not affected: a dot in the middle, used for women who carry an X-linked trait. | |
| Deceased: a diagonal line through the symbol. | |
| Proband: the arrow (often with a P) points to the person who brought the family to attention. | |
| Mating or partnership: a horizontal line between two partners. | |
| Consanguinity: a double line, when the partners are related by blood, such as cousins. | |
| Offspring: children hang from the parents' line, oldest on the left. |
Generations are numbered with Roman numerals down the left side (I, II, III), and people in each generation with Arabic numbers from left to right, so II-3 is the third person in the second generation.
How to read a pedigree
Ask three questions: does the trait appear in every generation or skip some? Are males and females affected equally? Can an affected father pass it to his sons?
Autosomal dominant
- The trait appears in every generation.
- Every affected person has at least one affected parent.
- Males and females are affected about equally, and fathers can pass it to sons.
- An affected parent with one copy of the gene passes it to each child with a 50% chance.
Autosomal recessive
- The trait often skips generations: affected children usually have two unaffected parents who are both carriers.
- Two carrier parents have a 25% chance with each child of an affected child, and a 50% chance of a carrier.
- Males and females are affected about equally.
- It shows up more often when the parents are related by blood.
X-linked recessive
- Many more males than females are affected.
- It is never passed from father to son, because fathers give their sons a Y chromosome.
- Affected males usually have unaffected mothers who are carriers; all daughters of an affected man are carriers.
X-linked dominant
- An affected father passes the trait to all his daughters and none of his sons.
- An affected mother passes it to each child with a 50% chance.
Mitochondrial
- Passed only through the mother, to all her children, although how strongly each child is affected can vary; affected fathers do not pass it on.
Draw your own
The pedigree chart maker draws pedigrees with these symbols, generation numbers and a key, and opens with an autosomal recessive example you can change. Looking for a genealogy pedigree chart, the form that lists your ancestors? See the pedigree chart templates.