How do I distinguish X-linked recessive from autosomal recessive?

Look for an affected female. In XR, an affected female MUST have an affected father and all her sons MUST be affected. If an affected female has an unaffected father, it is Autosomal Recessive.

What defines mitochondrial inheritance?

Mitochondrial traits are passed strictly from mothers to ALL their children. Affected fathers will never pass the trait to their offspring.

Vectora

Back to Biology Resources

Pedigree Analysis & Reasoning

Master the logic of pedigree analysis by stepping through classic genetic inheritance patterns found in biology exams.

About this simulation

What: An interactive Biology simulation of Pedigree Analysis & Reasoning.
Who: Designed for AP, IB, and A‑Level Biology students.
How: Runs in any modern browser — drag, adjust, and explore in real time.

Updated 2025-10-04

Key Concepts

Deductive Reasoning

Using specific family configurations to rule out certain inheritance modes (e.g., unaffected parents with an affected daughter rules out X-linked recessive).

Modes of Inheritance

The typical patterns: Autosomal Dominant (AD), Autosomal Recessive (AR), X-linked Dominant (XD), X-linked Recessive (XR), and Mitochondrial.

Probability Calculation

Once the mode is determined, using Punnett squares to calculate the risk for future offspring based on parental genotypes.

Pedigree Analysis Framework

Pedigree analysis is a core component of genetics. It requires identifying specific 'proof-positive' family configurations that can confirm or eliminate an inheritance hypothesis.

The golden rules: (1) If unaffected parents have an affected child, the trait is Recessive. (2) If recessive and an affected daughter has an unaffected father, it MUST be autosomal. (3) If affected parents have an unaffected child, the trait is Dominant.

Use the analyzer below to practice identifying these critical nodes and applying the logic systematically.