Build a family tree with standard genetic symbols, and this pedigree chart maker lays it out in textbook style, works out which inheritance pattern fits, infers genotypes and calculates the risk for the next child. Start from a template or an empty couple, tap a person to edit them, and download the finished chart as PNG or SVG.
A pedigree uses a small, fixed vocabulary. Males are squares, females circles, and a diamond stands for a person whose sex is unknown or not shown. A filled symbol means the person is affected, that is, shows the trait being traced. A central dot marks a known carrier, a diagonal line through the symbol means the person has died, and an arrow with a P points to the proband, the person through whom the family came to attention. Partners are joined by a mating line, doubled for blood relatives, with a vertical line down to their children; generations carry Roman numerals and individuals are numbered left to right, so II-3 is the third person in generation II.
Open Analysis and the tool tests all six patterns: autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked and mitochondrial. A pattern survives only if some assignment of genotypes to every person reproduces every phenotype, and the classic rules name the people behind each rejection. An affected child of two unaffected parents rules out both dominant patterns. Two affected parents with an unaffected child rule out both recessive patterns. An affected daughter with an unaffected father, or an affected mother with an unaffected son, rules out X-linked recessive; an affected father with an unaffected daughter rules out X-linked dominant, as does an affected son of an unaffected mother. Any affected female rules out Y-linked inheritance, and an affected child of an unaffected mother rules out mitochondrial inheritance. When several patterns survive, evidence such as male-to-male transmission or a generation skipped through carrier mothers picks the most likely one.
For the chosen pattern the Genotypes section prints every genotype each person can have, names the obligate carriers, and the Symbols | Genotypes switch writes them under the chart. Risk is computed by enumerating every consistent assignment under the textbook convention that founders carry as few copies of the rare allele as the chart allows, and weighting the assignments by Mendelian transmission. In the autosomal recessive template, first cousins III-2 and III-3 have two affected children, so both parents are obligate carriers and so are the grandparents II-2 and II-5 who link them to the common ancestors; the next child of the couple has a 1/4 chance of being affected and a 1/2 chance of being a carrier, and their unaffected daughter IV-2 has a 2/3 chance of carrying the allele. Under the X-linked recessive pattern a carrier mother’s next son has a 1/2 risk and her next daughter a 1/2 chance of being a carrier. Use the X-linked inheritance square to see those crosses cell by cell.
The maker traces one trait at a time, has no twin or adoption symbols, and assumes the allele is rare enough to enter the family only where the chart requires it, the standard textbook assumption but not always true for common alleles.
Squares are males, circles females and diamonds people of unknown sex. A filled symbol means the person shows the trait, a central dot marks a carrier, a diagonal line means deceased and a small arrow with a P marks the proband. A horizontal line joins partners, doubled when they are blood relatives, and a vertical line drops to the sibship line that holds their children.
Start from a template or an empty couple, tap a person and use the buttons: add parents, a partner, a child or a sibling, change sex and status, mark deceased or proband, and type a name. The layout, the generation numerals and the individual numbers update by themselves after every change, and undo takes you back if you slip.
Look at the affected females. An affected daughter of an unaffected father rules out X-linked recessive, because she must have received one X chromosome from him. If only males are affected, none of them has an affected father and the trait skips generations through unaffected mothers, X-linked recessive is the better fit, although autosomal recessive usually cannot be excluded outright.
Someone who shows no sign of the trait but must carry the allele because the pedigree leaves no other explanation, most often the unaffected parents of an affected child under a recessive pattern. The analysis lists them and prints their genotype as heterozygous.
The tool enumerates every genotype assignment that fits the phenotypes in the chart, keeps the ones in which founders carry as few copies of the rare allele as the pedigree allows, weights each by Mendelian transmission probabilities and sums them. For two carrier parents of a recessive trait that gives 1/4 affected and 1/2 carrier; for an unaffected sibling of an affected child it gives a 2/3 chance of being a carrier.
Yes. Download it as PNG or JPG with a legend for homework and reports, or as SVG for editing, and use the share button to copy a link that restores the whole family, including the chosen inheritance pattern.