What it does
A pedigree is a family tree that shows who has a trait. Squares are males, circles are females, filled symbols are affected, a horizontal line joins a couple and the lines below lead to their children. Reading one is like detective work: each pattern of inheritance leaves its own fingerprints.
- The family. Three generations: grandparents I-1 and I-2, their children II-1, II-3 and II-5, the partners who married in (II-2 and II-4), and four grandchildren. Tap anyone to mark them affected or unaffected. Switch to Tap: boy or girl to change the sex of a child.
- The verdicts. For each of five patterns (autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked) the page tries every possible set of genotypes, assuming one gene and that everyone who carries a dominant allele, or two recessive ones, shows the trait. A pattern fits if at least one set works.
- Why not? A ruled-out pattern names the family that breaks it, for example “II-5 is affected but neither parent is: a dominant trait cannot skip a generation”.
- Carriers. Tap a pattern that fits and a dot appears inside everyone who must be a carrier under it. When several patterns fit, the note counts how many unrelated carriers each would need to marry in: for a rare trait, fewer is more likely.
This fits Class 12 Biology: principles of inheritance and variation (pedigree analysis, sex-linked inheritance, Mendelian disorders) and builds on Class 10 Science: heredity. Start with dominant and recessive alleles in mendel's pea garden; work out exact odds for any cross with the punnett square; and to draw a real-size family tree of your own, use the pedigree drawing tool.
How to use it
- Tap an example family, or mark people yourself.
- Read the list of patterns: green ticks fit, red crosses are ruled out with a reason.
- Tap a pattern in the list to see its carriers in the tree.
- Change a grandchild from boy to girl and watch the X-linked verdicts change.
- Try the Check yourself questions.
Worked example
“Skips a generation”: II-5 and his niece III-4 are affected, but none of their parents are. A dominant trait can’t hide, so autosomal dominant is ruled out (II-5 is affected but neither parent is). III-4 is a girl with an unaffected father, so X-linked recessive is ruled out too: she would need the allele on her father’s X. Only autosomal recessive fits, and the dots show the carriers: I-1, I-2, II-3 and II-4.
“Sons of carrier mothers”: grandfather I-1 and grandson III-3 are affected. X-linked recessive fits, with II-3 an obligate carrier: she got her father’s X. Autosomal recessive also fits, but it needs II-4, who married into the family, to be a carrier too, which is unlikely for a rare trait. Make III-3 a girl and X-linked recessive drops out.
Tips
- Affected children of unaffected parents: recessive. Unaffected children of two affected parents: dominant.
- Mostly males affected, passed through unaffected daughters: think X-linked recessive.
- An affected father whose daughters are all affected and sons all unaffected: think X-linked dominant.
- Father to every son, never to daughters: Y-linked.
FAQ
Why can several patterns fit? Small families often don’t contain the one mating that would rule a pattern out. Real geneticists look at many families and at how rare the trait is.
Does it handle traits that skip people who carry a dominant allele? No. It assumes full penetrance and one gene, as school questions do.
Is anything saved? No. Everything runs in your browser and nothing is stored or sent.
Is this an official textbook tool? No. It is an independent practice page that follows the same school topics.
Where the numbers come from
- Pedigree symbols and the rules of autosomal, X-linked and Y-linked inheritance with full penetrance are standard genetics. The verdicts come from trying every genotype for every person; this was checked in the tests against an independent Python brute force on 40 random families, and the one-line reasons were checked against it on 5000 more.
- The example families are made up for teaching and describe no real people or disorders. This is a learning tool, not genetic counselling. Drawings are fibub's own. Nothing you enter is stored or sent anywhere.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.