AP Biology LAB NATURAL SELECTION OF “STRAWFISH”

AP Biology LAB NATURAL SELECTION OF “STRAWFISH” You have already been introduced to the idea that when an organism is “selected by nature” to survive, it then has the opportunity to reproduce and pass on the genes for its favorable traits to its offspring. In this way, the genes for more favorable traits — traits that give an individual organism greater fitness — show up more frequently in each succeeding generation. In this activity, we will explore this concept further. Our model organism, in this lab, will be a species of fish — the “Strawfish” — that live in freshwater ponds. In this simulation, we will investigate how different natural selection factors in the environment can influence the colors of Strawfish. We will also look “underneath the skin” and measure how these natural selection factors also affect the inheritance of the genes that code for the color of Strawfish. In Strawfish, there are three scale/skin colors (phenotypes)— blue, yellow, green. These three colors are controlled by a color gene that comes in two versions (two alleles) — the blue allele and the yellow allele. The blue and yellow alleles do not show a classical dominant / recessive interaction. Instead when they are inherited together they show an incomplete dominance interaction, therefore the heterozygote will be a green colored fish. Each lab group (working in pairs) will be given a bag of alleles (straws) — 20 yellow and 20 blue straws. These represent the collection of genes in our population of fish — the fish gene pool. As in nature, Strawfish are diploid organisms — they have two copies of every gene. The color of each fish is always determined by the interaction of the two copies (the two straws). On the chart, indicate the possible genotypes (straw colors), for each phenotype (fish color) Phenotype Genotype yellow fish YY blue fish BB green fish BY In each part of the lab, you will create fish by randomly pulling out two straws to determine their skin color. Each group will complete four different scenarios simulating different selection factors affecting your population of Strawfish. Ready? Let’s go fishing! GENERAL INSTRUCTIONS: RULES FOR FISHING 1. First make sure there are 40 straws in your bag (20 blue & 20 yellow). 2. In each round, you will randomly pull two straws (alleles) from your fishing bag for each fish in the population and record the color of the resulting “Strawfish” in your data table until the bag is empty. 3. The first round in all tests serves as a control and should be completed without any predation. In the next three generations in each test, predators will prey on the fish but under different selection factors (selection rules)