OVERVIEW

I. Genotype and Phenotype
The concept of how genes influence our traits is introduced by discussing simple traits the students can observe in themselves and their classmates. 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 using height as an example. 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. The phenotype of offspring and parents is discussed.

In small groups, the students rotate between 3 work-stations. Station 1: students use microscopes to examine nematodes with visible genetic differences. Station 2: in vials, students examine fruitflies with different phenotypes and observe the 3 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. Papillae can be observed using blue food coloring and a flashlight.

II. 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.

In small groups, the students rotate between 3 stations. Station 1: examine with microscopes slides of onion cells or whitefish blastula at different stages of mitosis. Station 2: each group is given pictures of human karyotypes (visible chromosomes) and asked to distinguish normal male and female cells and Down’s syndrome cells, which carry an extra chromosome. Station 3: the students are shown a video of actual mitosis. Also, the number of genes in different organisms is discussed.

III. DNA and Molecular Biology
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 is discussed as well as differences in sequence between individuals. Different forms of the genes are called alleles.

In small groups, students learn how DNA is analyzed using restriction enzymes that recognize certain sequence motifs. They perform agarose gel electrophoresis to determine if a piece of DNA is cut by the enzyme and therefore has the sequence motif. DNA sequence analysis is illustrated with the students participating in reading genetic sequence from lab films. Applications of this technology are also discussed.