Non-Mendelian Genetics

Non-Mendelian Genetics is topic 5.4 of AP Biology, inside Heredity. This page works through three real practice questions on it, with the full reasoning behind each credited answer.

Practise this topic freeThe whole unit
52 questionsStatistical Tests and Data Analysis81% with a figure
Worked examples

Three real non-mendelian genetics questions

From the practice pool, not the mock papers — each with the reasoning that produces the answer.

81% of them come with a figure. Reading the graph or diagram correctly is most of the work here before any content knowledge applies.

Statistical Tests and Data Analysis · with figure

In a testcross for two linked genes, the offspring counts are shown. What is the approximate recombination frequency?

  1. A5.9%; using only recombinant type 2
  2. B12%; using both recombinant classes out of all offspringcorrect
  3. C44%; using one parental class as the numerator
  4. D6.1%; using only recombinant type 1
Why B is correct

Recombinant offspring total 61 + 59 = 120 out of 1000 total offspring. The recombination frequency is 120/1000 x 100% = 12%.

The stem asks for a numerical or quantitative judgment: "In a testcross for two linked genes, the offspring counts are shown. What is the approximate recombination frequency". The safe route is to identify the counted event, use the full denominator, and then interpret the number biologically. Here the worked reasoning is Recombinant offspring total 61 + 59 = 120 out of 1000 total offspring, so choices based on 5.9%; using only recombinant type 2 or 44%; using one parental class as the numerator lose the required setup.

Statistical Tests and Data Analysis

In a cross AaBb x aabb, the genes assort independently. What is the probability of producing an offspring with genotype Aabb?

  1. A1/2; counts only the A allele from the heterozygous parent
  2. B1/8; multiplies by an extra allele event after choosing Ab
  3. C1/4; only the Ab gamete from AaBb produces Aabbcorrect
  4. D1/16
Why C is correct

The AaBb parent produces AB, Ab, aB, and ab gametes with equal probability. The aabb parent produces only ab gametes. Aabb results when the first parent contributes Ab, which occurs with probability 1/4.

The stem asks for a numerical or quantitative judgment: "In a cross AaBb x aabb, the genes assort independently. What is the probability of producing an offspring with...". The safe route is to identify the counted event, use the full denominator, and then interpret the number biologically. Here the worked reasoning is Aabb results when the first parent contributes Ab, which occurs with probability 1/4, so choices based on 1/2; counts only the A allele from the heterozygous parent or 1/8; multiplies by an extra allele event after choosing Ab lose the required setup.

Statistical Tests and Data Analysis · with figure

A coat-color gene has a dominance hierarchy C > cch > ch > c. A parent with genotype Cc is crossed with a parent with genotype cchc. In a model of 80 offspring, how many are expected to show the C phenotype?

  1. AHalf of the offspring inherit C from the Cc parentcorrect
  2. B0 offspring, because C cannot be inherited with cch or c
  3. CC is dominant over all listed alleles
  4. D60 offspring, because every offspring except cc must show the C phenotype
Why A is correct

The Cc parent contributes C to half of offspring and c to half. Any offspring inheriting C will show the C phenotype, so half of 80, or 40 offspring, are expected to show that phenotype.

The stem asks for a numerical or quantitative judgment: "A coat-color gene has a dominance hierarchy C > cch > ch > c. A parent with genotype Cc is crossed with a parent...". The safe route is to identify the counted event, use the full denominator, and then interpret the number biologically. Here the worked reasoning is Any offspring inheriting C will show the C phenotype, so half of 80, or 40 offspring, are expected to show that phenotype, so choices based on 0 offspring, because C cannot be inherited with cch or c or 80 offspring, because C is dominant over all listed alleles lose the required setup.

52 questions on this topic, free to start.

Ten a day at no cost. One account covers SAT, ACT and AP.

Start free
Last reviewed 2026-08-28. Topic and unit names follow the College Board course framework. Question counts describe the PrepScore practice bank, not the exam.
Same unit
Chromosomal Inheritance37 questionsMendelian Genetics22 questionsEnvironmental Effects on Phenotype21 questions

Work non-mendelian genetics until the reasoning is automatic.

Real AP questions with a full explanation on every answer, and a mistake bank that only clears when you get it right.

Start freeBack to the unit