16.1: Instructor Guidelines
- Page ID
- 118033
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This lab provides a basic introduction to Mendelian genetics for students. In Part 1, students are introduced to genetics vocabulary terms, including heterozygous, homozygous, dominant, and recessive. Practice problems integrating Punnett squares allow students to compare typical inheritance patterns with incomplete dominance and codominance. Students will also be able to compare the genotypic and phenotypic ratios seen in monohybrid versus dihybrid crosses.
Tasks
Students will complete the following during this lab:
- Investigate patterns of Mendelian genetics using Punnett squares and alleles representing the following:
- Typical inheritance patterns
- Incomplete dominance
- Codominance
- Compare and contrast the genotypic and phenotypic ratios of monohybrid vs. dihybrid crosses.
- Use phenotypic traits to derive potential genotypes and relative frequencies in the classroom population.
Lab instructors should provide students with an introduction to Mendelian genetics and the related vocabulary terms. Going over at least one practice problem of each type as a class will help provide a guide for students to complete the remaining problems.
In your introduction to the lab, provide students with sample images of the physical traits (e.g. tongue rolling, widow's peak, etc.) as many students will be unfamiliar with these terms. Once the percentages of dominant and recessive phenotypes for the class are calculated, students will be able to see that dominant alleles are not always more common (both in the class and in the general population).
In Part 2, the dihybrid cross, students generally have a difficult time understanding how to create gametes when two characters are involved. Remind students that each gamete must have at least one allele for each character. For instance, an AaBb parent could form the following gametes: AB, Ab, aB, or ab. Here, students often make the mistake of creating gametes such as the following: AA, BB, Aa, etc. Creating connections between meiosis and the gametic alleles may be helpful.
Finally, encourage students to recognize (memorize) major genotypic or phenotypic patterns. Recognizing the 1:2:1 genotypic and 3:1 phenotypic ratio in the progeny for a monohybrid cross and the 9:3:3:1 phenotypic ratio in the progeny for a dihybrid cross will be helpful as students progress to more challenging genetics problems.