Definition
What is a pedigree?
A pedigree is a diagram of a family's relationships across several generations that records which members have a particular trait or genetic condition. Geneticists draw pedigrees with standard symbols: squares for males, circles for females and diamonds when sex is unknown. A filled symbol marks an affected person and a half-filled one a known carrier. A horizontal line joins two partners, a double line marks partners who are blood relatives, and vertical lines lead down to their children. Generations are usually numbered with Roman numerals.
Because people cannot be crossed like pea plants, pedigrees are the main way to study inheritance in human families. Their shape points to the mode of inheritance. An autosomal dominant trait tends to appear in every generation, an autosomal recessive one often skips generations and can turn up in children of unaffected parents, and an X-linked recessive one mostly affects males. The affected person who first brings the family to medical attention is called the proband.
Pedigrees are central to genetic counseling, where they help estimate the chance that a condition will recur. The word comes from Old French for 'crane's foot', after the branching lines of early family charts.
Word parts
Where does the word “pedigree” come from?
- pé de grue
- crane's footAnglo-French, from Latin pes 'foot' and grus 'crane'
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Terms that go with it
- Mendelian inheritanceMendelian inheritance is the pattern by which single genes pass from parents to offspring, following the laws of segregation and independent assortment.
- Dominant alleleA dominant allele is a version of a gene whose effect shows in the phenotype even when only one copy is present, masking a recessive allele.
- Recessive alleleA recessive allele is a version of a gene whose effect appears only when an organism has two copies, because a single dominant allele masks it.
- GenotypeA genotype is the genetic makeup of an organism, either at one locus, such as Aa, or across its whole genome, including alleles it does not express.
- PhenotypeA phenotype is the set of observable traits of an organism, such as its height or blood group, produced by its genotype acting with its environment.
- AlleleAn allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.
Sources
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Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Pedigree
- LibreTexts, Online Open Genetics (Nickle and Barrette-Ng), 5.2 Pedigree Analysis
- MedlinePlus Genetics: What are the different ways a genetic condition can be inherited?
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