Please review these General Instructions for some general classroom guidelines.
Genotype and Phenotype
- The concept of how genes influence our traits is introduced by discussing simple traits that students can observe in themselves and their classmates (ability to roll the tongue, hitchhiker’s thumb). Ask students where do we get our genes and how many copies of every gene?
- Using some examples, we explain how genes inherited from their parents (genotype) determine their trait (phenotype).
- The role of environment in influencing traits is also discussed.
- Then we discuss complex traits such as height that is determined by both genes and environment.
- Volunteer students participate in a hypothetical mating in which a coin toss is used to demonstrate the probability of receiving a particular allele from each parent (50:50).
- The phenotype of offspring and parents is discussed as each side of the coin is marked with R or r.
In small groups, the students rotate between 3 workstations.
- Station 1: students use microscopes to examine nematodes with visible genetic differences.
- Station 2: students examine fruit flies with different phenotypes and observe the developmental stages: larvae-pupae-adult.
- Station 3: the students test their ability to taste phenylthiocarbamide (PTC) paper and correlate this with the number of fungiform papillae (containing taste buds) on their tongue. Students also learn about the role of smell in taste using an exercise with a jellybean.
Chromosomes and Mitosis
- The concept that genes are located on chromosomes is introduced.
- Chromosomes can be visualized with microscopes during certain stages of cell division.
- Together, the class reviews cellular division and goes over what happens to the chromosomes during the different stages of mitosis.
- Volunteer students act out chromosome segregation: Two students act as chromosomes and two as centrioles. The two chromosomes are attached to each other with toilet paper (centromere) and to the two students representing centrioles with string (spindle fibers). The chromosomes get pulled apart to the two daughter cells and the toilet paper breaks. Students then view 5 minute video on mitosis. Students view and discuss pictures of normal male and female karyotypes and then an abnormal karyotpye (trisomy).
- The structure of DNA using a double helix model is explained.
- The nature of DNA sequence, (4 bases ATCG, and sugar-phosphate molecules) as the basic composition of a gene and the complementarity of the two strands with A =T and C = G pairing is discussed. We have a model of DNA and students read off the sequence from one strand and then the other strand. Different forms of a gene result from differences in sequence. We illustrate with the dominant allele R and recessive allele r, which determine whether a person can roll their tongue (from lesson 1). Then the idea of reading the sequence to obtain information about what proteins to make is discussed.
- We play a game called “who Ate the Cookies” to illustrate the idea of using DNA to identify people.
- Can discuss applications of this information.
- In small groups we make DNA bracelets using cells from inside student's cheek for the source of DNA.