Salamander Spots: Patterned or Not?

Preparation

• Students should have a grasp of Mendelian and non-Mendelian genetics.
• This activity is most appropriate for students with a background in Algebra II, although general level classes can complete the lesson by comparing the ratios of individuals possessing each spot pattern.
• Background information for the concepts used in this lesson can be found in the “References” section below.

Part I – Observation and Hypothesis

1. Explain that in this vernal pool there is a single population of spotted salamanders but they congregate randomly into several mating groups. Show Video 1 of spotted salamanders. Teacher asks students to focus on the array of spots seen along the back of the salamanders. After viewing Video 1 a few times to understand the group, develop a hypothesis about the spot patterns.
2. Use the interactive images to assist students in identification of spot patterns.
3. After the hypothesis is developed, freeze the video at a clear view. Students make the observations: N = total number of individuals in the frozen view, count and record the number of alternate, opposite, and random spot patterns. Provide students the data table for recording spot patterns.
4. Proceed to Video 2. Repeat the process of viewing, complete a new data table, freeze, count, and record.
5. Proceed to Video 3. Repeat the process of viewing, complete a new data table, freeze, count, and record.
6. Calculate the spot arrangement ratios for each mating mass. Consider each mating mass ratio: Does there appear to be a preference for any one pattern with each group?
7. Collate all three data sets and calculate spot arrangement ratios for the entire population of spotted salamanders in this vernal pool.

Part II – Data Collection

1. Students view a selection of video clips of spotted salamander mating masses within a single population. They are asked if there is a pattern that can be discerned. Students may need to be guided to classifying spot patterns as alternate, opposite, or random. View Video 1. Movement makes it difficult to count individuals and discern their spot patterns. Pause video where most salamanders are visible. Count individuals visible (N). Observe spots for pattern or not. Create data table with salamander numbers (1,2,3…) and choice of pattern (alternate, opposite, random).
2. Students return to the paused video to classify the frequency of spot patterns in this mating mass image.
3. Teacher concludes this session by asking if one spot pattern seems to be prevalent? Is there a pattern that is less common? Can the spot pattern be quantified into a rough ratio?
4. Proceed to Video 2. Repeat the process of viewing, complete a new data table, freeze, count, and record.
5. Proceed to Video 3. Repeat the process of viewing, complete a new data table, freeze, count, and record.
6. Calculate the spot arrangement ratios for each mating mass. Consider each mating mass ratio: Does there appear to be a preference for any one pattern with each group?
7. Collate all three data sets and calculate spot arrangement ratios for the entire population of spotted salamanders in this vernal pool.
8. Teacher reviews patterns of genetic inheritance. Based upon the visual evidence, does the pattern of spots seem to follow a pattern of inheritance? Which pattern seems to best fit the data?
9. Teacher introduces the idea of the Chi-Squared test. Are spot patterns controlled by genetics? Does the inheritance follow a simple dominant recessive pattern? Is the occurrence of spot patterns seen random?

Part III – Evaluation

• Have students revisit their original hypotheses.
• Have them write a conclusion document that either confirms or refutes their hypotheses based on their data table and analysis. Have them include all statistical analyses used (total each type, ratio of spot patterns, Chi-squared test).

Note: Conclusion should discuss whether the number of individuals viewed can be considered indicative of the entire spotted salamander population or just for the population that utilizes this particular vernal pool.