AP Biology Unit 5 Topic 2: Mendelian genetics

What to Know

Alleles separate during gamete formation, so offspring inherit one allele from each parent.
Punnett squares model probability, not guaranteed outcomes for a small number of offspring.
The expected phenotype ratio depends on the genotypes of the parents and the dominance relationship.
Always connect this topic back to the larger unit: Heredity.

Detailed Notes

Mendelian genetics belongs to Unit 5: Heredity. Mendelian genetics predicts inheritance patterns for traits controlled by single genes with clear allele relationships. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Alleles separate during gamete formation, so offspring inherit one allele from each parent. Punnett squares model probability, not guaranteed outcomes for a small number of offspring. The expected phenotype ratio depends on the genotypes of the parents and the dominance relationship.

Model to use: Use a monohybrid or dihybrid cross to connect parental genotypes with expected offspring probabilities. 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: For genetics problems, define the alleles, write parent genotypes, make gametes, then calculate and interpret probability. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.

Key Vocabulary

Allele

A version of a gene.

Genotype

The allele combination an organism has for a gene or set of genes.

Phenotype

The observable trait or measurable expression of a genotype.

Dominant trait

A trait expressed when at least one dominant allele is present.

Recessive trait

A trait expressed when no dominant allele masks it.

Testcross

A cross used to determine an unknown genotype by pairing it with a homozygous recessive individual.

Quick Practice

How would you explain Mendelian genetics 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.