AP Biology Unit 5 Topic 3: Non-mendelian Inheritance

What to Know

Incomplete dominance and codominance produce phenotype patterns that differ from complete dominance.
Multiple alleles, sex linkage, and polygenic inheritance can change expected ratios.
Gene interactions and environmental effects can make inheritance patterns more complex than a single Punnett square suggests.
Always connect this topic back to the larger unit: Heredity.

Detailed Notes

Non-mendelian Inheritance belongs to Unit 5: Heredity. Many traits do not follow simple dominant-recessive patterns because genes can interact in more complex ways. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Incomplete dominance and codominance produce phenotype patterns that differ from complete dominance. Multiple alleles, sex linkage, and polygenic inheritance can change expected ratios. Gene interactions and environmental effects can make inheritance patterns more complex than a single Punnett square suggests.

Model to use: Compare expected phenotype ratios under complete dominance, incomplete dominance, codominance, and sex linkage. A clear model should label the parts, show the direction of movement or information flow when relevant, and connect the diagram back to the biological outcome.

AP-style move: When observed data do not match a simple Mendelian ratio, propose a different inheritance pattern and justify it with evidence. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.

Key Vocabulary

Incomplete dominance

An inheritance pattern in which heterozygotes show an intermediate phenotype.

Codominance

An inheritance pattern in which both alleles are visibly expressed in heterozygotes.

Multiple alleles

More than two allele forms existing in a population for one gene.

Polygenic inheritance

A trait pattern influenced by multiple genes.

Sex-linked trait

A trait associated with a gene on a sex chromosome.

Epistasis

A gene interaction in which one gene affects the expression of another gene.

Quick Practice

How would you explain Non-mendelian Inheritance in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

Biology concept reference: Biology for AP Courses by OpenStax, Rice University. Access for free at OpenStax. Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. EduCompanion used this source as a conceptual reference and rewrote the study notes in original wording.