9.1: Introduction
Geneticists breed organisms with different characteristics, or phenotypes, to answer questions about how the phenotypes are inherited. Is one phenotype dominant and one recessive? Is each phenotype controlled by a different version (allele) of a single gene, or are many interacting genes involved? In this activity, you will answer these questions by analyzing the outcome of breeding a stickleback with pelvic spines and one without pelvic spines—the same procedure, called a genetic cross, that Dr. David Kingsley described in the film Evolving Switches, Evolving Bodies.
The fish shown in the photo above is a marine three spine stickleback. Like all marine and sea-run stickleback, this fish has a pair of pelvic spines (only one is visible in the photo), which serve as a defense from large predatory fish. In some freshwater populations, such as in Bear Paw Lake, Alaska, stickleback lack pelvic spines. (The scale is in centimeters.) How are these two phenotypes inherited?
Analyze a Stickleback Trait
Materials
- Stickleback trait sheet
- F 1 stickleback fish cards
- F 2 stickleback fish cards
Procedure
Watch the short film entitled The Making of the Fittest: Evolving Switches, Evolving Bodies
( https://www.youtube.com/watch?v=Pv4Ca-f4W9Q&feature=youtu.be )