AP Bio · Unit 5 Progress Check

AP Biology Unit 5 Progress Check Heredity walkthrough.

AP Biology Unit 5 is heredity, and the Unit 5 Progress Check MCQ leans on Punnett squares, pedigrees, and the chi-square test. This walkthrough explains what each question type is testing, the traps that cost points, and how to work through them. Explanations only — we never publish AP Classroom answer keys.

Updated August 2026Written by Mahmudul HasanFree · No signup

What Unit 5 covers

Unit 5 is Heredity. Heredity is roughly 8–11% of the AP Biology exam and supplies a recurring chi-square free-response question.

Meiosis

How gametes form, and how crossing over and independent assortment create variation.

Mendelian genetics

Segregation, independent assortment, monohybrid and dihybrid crosses.

Non-Mendelian inheritance

Incomplete dominance, codominance, multiple alleles, polygenic and sex-linked traits.

Pedigree analysis

Reading family trees to infer whether a trait is dominant, recessive, or sex-linked.

Chi-square

Testing whether observed offspring ratios differ significantly from expected.

Environmental effects

How environment influences phenotype expression.

The Progress Check MCQ: what each question type tests

These are the question patterns that recur on this Progress Check, and what each one is really asking.

Cross prediction

Set up the Punnett square properly — most errors are in the parental genotypes, not the arithmetic.

Pedigree inference

Look for an affected child of unaffected parents (recessive) and check whether males are disproportionately affected (X-linked).

Chi-square reasoning

Usually conceptual: does the value exceed the critical value, and what does that mean about the null hypothesis?

Non-Mendelian recognition

A 1:2:1 phenotype ratio signals incomplete dominance or codominance, not simple dominance.

Meiosis errors

Nondisjunction questions ask which stage produced an abnormal gamete.

The Progress Check FRQ

Unit 5 free response frequently asks for a chi-square analysis: state the null hypothesis, calculate the expected values, compute the statistic, compare it against the critical value at the correct degrees of freedom, and then say what that means biologically. Points come from the full chain, not the number.

Where students lose the most points

Getting degrees of freedom wrong

df = number of phenotype categories minus 1 — not the number of organisms.

Skipping the null hypothesis

The chi-square conclusion is meaningless without stating what you were testing.

Confusing genotype and phenotype ratios

A 3:1 phenotype ratio comes from a 1:2:1 genotype ratio.

Assuming sex-linked means male-only

Females can be affected; they just need two copies for a recessive X-linked trait.

Concluding “the data is wrong”

A significant chi-square means reject the null hypothesis, not that the experiment failed.

How to work through this unit

For chi-square, write the null hypothesis first and the degrees of freedom second, before touching the calculator. Those two steps carry most of the rubric points.

Once you have finished the Progress Check, put your raw score into our AP Biology Calculator to see roughly where that pace puts you on the 1–5 scale, and use the AP Biology Review for the full exam format and study plan.