Mark Collins

How we write a genetics question

Blog Post created by Mark Collins on Jun 6, 2016

As biology students progress to upper division classes, they move away from the stylistic foundation set by introductory biology courses. Memorization of terms and concepts, while important for understanding biological science, gives way to quantitative reasoning. This transition can be difficult for many students, as genetics is seen as a springboard course for developing scientific skills.

A foundation in biology allows students to build problem solving, critical thinking, and data analysis skills. Here is how Sapling Learning fosters skills like these in our genetics questions, and makes sure every student comes to class prepared.

Question Stem

Take the question below, in which a student is given a trait of interest, the experimental setup, and the phenotype data for different types of crosses. She is then asked to predict the mode of inheritance from the expected offspring ratio in four distinct scenarios. The student needs to understand the “how” as well as the “why” for each allele interaction in these inheritance scenarios.


First, the student must read and understand the experimental setup. She must infer that the F1 progeny are all heterozygous because both parental strains were homozygous for a particular trait, in this case tail length.

The student may begin by tackling the autosomal crosses. The offspring of the F1 x F1 heterozygote cross can inherit any of the three combinations of dominant and recessive alleles; AA, Aa, or aa. When the short tailed allele is recessive only the aa genotype would produce a short tailed phenotype. When the short tailed allele is dominant, both homozygous AA and heterozygous Aa offspring present the short tailed phenotype. For sex-linked dominant and recessive modes of inheritance, the heterozygosity of female and hemizygosity of the male offspring differs from the mendelian 3:1 phenotypic ratio.

Preliminary Help

Let’s assume the student isn’t quite sure how to get started on this problem. She simply clicks “Hint” at the bottom left of the question page to open a panel with some additional information to help her think about the four concepts that are combined within this question.


The hint introduces the concepts of chromosome type and dominance type. The dominance type describes the relationship between different alleles of a gene. The chromosome type describes limitations based on whether the gene is found on an autosome or sex chromosome.

The hint also provides an action item of “Draw Punnett squares…” to put the student’s knowledge into action. If extra guidance is needed, a Punnett square interactive provides a workspace that will assist the student in drawing the squares using this method.

Targeted Instructional Feedback

Once the student clicks “Check Answer”, her answer is submitted and recorded. If she gets it wrong, Sapling Learning has already predicted possible misconceptions she might have with the concepts being tested and has provided targeted instructional feedback to guide the student from her misconception toward the correct solution.

One possible misconception is that the student may switch the concepts of dominant and recessive alleles. She is reminded that if the short allele were dominant, the heterozygote would be phenotypically short-tailed, whereas if the short allele were recessive, the heterozygote would be phenotypically long-tailed.

Another possible misconception is swapping the autosomal and sex-linked chromosomal modes of inheritance. In this situation the student is advised that a male is XY, so only one copy of the allele, on the X chromosome, is present to be expressed.


Each answer choice is also addressed with individually tailored feedback. For example, if the student does not correctly identify that an autosomal recessive mode of inheritance produces an offspring ratio “3 long : 1 short”,  she will be guided toward this choice. The feedback does this by indicating that heterozygous offspring would have long tails. It also address the distinction between an autosomal recessive and a sex-linked recessive mode of inheritance.

Worked-out Solution

Once the student correctly matches the expected offspring ratio for each mode of inheritance, and clicks “Check Answer”, she reaches the answer and solution. The solution lays out a clear and complete explanation of the problem. It guides the student through the logic of each mode of inheritance, with four Punnett squares illustrating the four ideas presented in this question.

To ensure that misconceptions do not persist, the solution also addresses incorrect choices, even if a student answered the question correctly on their first attempt. The solution and targeted feedback are saved for a student to come back and review, before class or even before an exam.


Impact to Students

Sapling Learning’s online homework for genetics aims to help students develop and apply a new skill: scientific thinking. First, we reinforce the concepts you teach in lecture by providing specific starting points for students to approach the problem that are easily accessible within the question itself.

Students need to infer data from the text and practice skills mastered in class to generate Punnett squares and solve the four related concepts. If mistakes are made, our targeted feedback corrects misconceptions and provides distinct guidance to the correct answer. This feedback can lead students to illuminating moments in the problem solving process.

Once the problem is complete, a detailed solution address all of the relevant concepts and works through the logic of each, allowing students to concept check and see how the problem should be approached as they journey away from rote memorization.