• describe hypothesis testing and why HWE is a null hypothesis; and
• construct graphs and tables to understand the effects of natural
selection and/or genetic drift on allele and genotype frequencies
in a population over time.
Description of Activity
Our two-part activity makes use of “just-in-time” teaching (Novak,
2011), hands-on learning, and connections to authentic research data.
The activity contextualizes HWE through the evolution of toxin-resistance in the soft-shell clam, Mya arenaria, an Evo-Ed Case
( http://www.evo-ed.org; White et al., 2015). Students are not expected
to have prior knowledge about this case, thus enabling them to “
discover” differences in their populations and the driving evolutionary
forces in real time. The Evo-Ed website provides curricular materials
to support teaching evolution as an integrated process, connecting
events across biological scales, from nucleotides to populations. We
used this framework to develop and test our activity addressing HWE
in actual populations, with a trait where the complete pathway (genes→
proteins→ phenotype→ fitness→ selection) is known. Part 1 of the activity introduces HWE in the context of clams spawning in the ocean;
part 2 illustrates the effects that selection and drift can have on allele
frequencies within clam populations across generations.
We implemented the clam activity in one upper-level evolution course
(14 junior/senior biology majors) and two introductory-level survey
courses (71 first-year biology majors; 28 sophomore biology majors)
across three diverse institutions in the northeastern and southeastern
United States. In the evolution course, the two parts of the activity
were implemented over two consecutive 55-minute class periods. In
both introductory-level courses, students completed the entire activity
in one 3-hour lab session.
Activity Part 1: Clam Spawning
The following materials are required (Figure 1):
• Bag of 100 red marbles/beads
• Bag of 100 yellow marbles/beads
• Bag of 100 mixed marbles/beads, 50% red and 50% yellow
• Shared spreadsheet to record student spawning data (http://
• Worksheet that students complete during the activity and discussion
(Figure 2; http://evo-ed.org/pages/resources.html#abt_resources)
Students act as individual soft-shell clams in a classroom population that represents an idealized population that experiences no
selection, migration, mutation, drift, or nonrandom mating ( i.e., it
fulfills the requirements of HWE). The activity proceeds as follows:
• Each student entering the classroom chooses a handful of beads
from one of three bags: red, yellow, or mixed. These beads represent the clam gametes that each student will subsequently
broadcast out into the spawning environment.
• Students record their spawning gametes ( i.e., numbers of red
and yellow) and place them in a community bucket.
• The instructor records the total number and color of student
gametes in the bucket on a class spreadsheet.
Here, the instructor may choose to spend a few minutes
describing how clams reproduce by releasing gametes into the
water column (broadcast spawning). This teaching and learning
can be augmented with textbook materials or an online video on
broadcast spawning. Although the primary goal is to introduce
HWE, this activity introduces it through basic probabilities, a
Figure 1. Supplies needed for clam HWE activity.
Figure 2. Example student worksheet for clam HWE activity
part 1 (see additional resources at http://evo-ed.org/pages/