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Tim Guilfoyle Go [email protected] Phillip O. Berry Academy Charlotte, NC 28075 Using Genetic Crosses to Analyze a Stickleback Trait • Is one phenotype (with spines or without spines) dominant and one recessive? • Students apply the principles of Mendelian genetics to analyze the results of genetic crosses between stickleback fish with different traits, or phenotypes (with and without spines). • Students will use photos of actual research specimens to obtain their data; they will then analyze additional research data from the scientific literature. The fish shown in the photo on the left is a marine threespine stickleback. Like all marine stickleback, this fish has a pair of pelvic spines (only one is visible), which serve as a defense from large predatory fish. In some freshwater populations stickleback lack pelvic spines. (The scale is in centimeters.) The Making of the Fittest: Evolving Switches, Evolving Bodies The Making of the Fittest: • • • • Evolving Switches, Evolving Bodies Freshwater stickleback populations were established when marine populations became trapped in lakes, initially connected to the ocean, that formed at the end of the last ice age. Freshwater stickleback fish underwent many “changes” (color, size, skeleton) as they adapted to life in freshwater. The presence of different predators in different lakes dictated the subsequent evolution of each isolated lake stickleback over the course of about 10,000 years. Some groups “kept” their spines to use against predatory fish while others “lost” their spines, perhaps to evade aquatic insect predators. The Making of the Fittest: Evolving Switches, Evolving Bodies In the ocean there are lots of large predatory fish and there is no place to hide. The Making of the Fittest: Evolving Switches, Evolving Bodies The Making of the Fittest: Evolving Switches, Evolving Bodies They’re generally easy for predatory fish to catch but they’re not easy to swallow. The Making of the Fittest: Evolving Switches, Evolving Bodies Using Genetic Crosses to Analyze a Stickleback Trait Stating the Hypothesis: Which Phenotype Is Dominant? Examine the offspring of a genetic cross between a stickleback from the ocean (marine stickleback) and a freshwater stickleback from Bear Paw Lake. 1. Based on what you learned in the film, what are the phenotypes of these two parental stickleback fish? Indicate your choice with a check mark. Marine __ pelvic spines present __ pelvic spines absent Bear Paw Lake __ pelvic spines present __ pelvic spines absent 2. If we start with the simplest assumption that the presence or absence of pelvic spines is controlled by a single gene with two alleles, how would you denote the genotype of the two homozygous parents? PP X pp What is your hypothesis for which phenotype is dominant and which one is recessive? Assign Genotypes: PP or pp Marine __________________ PP or pp Bear Paw Lake _________________ Based on your hypothesis, what would you expect to be the results of the cross between the Marine and Bear Paw Lake stickleback parents? Answer depends on which phenotype is hypothesized to be dominant (with spines or without spines); however 100% of F1 will be heterozygous (1:0 ratio) What do you expect would be the result of crossing two F1 fish to produce the second filial (F2) generation? 3:1 ratio If you had 40 offspring in the F2 generation, approximately how many would you expect to have pelvic spines and how many to lack pelvic spines? 30 : 10 (with spines and without spines or vice versa depending on the students hypothesis) Obtaining the Data: Do the Results from the Experiment Support Your Hypothesis? • Now you will use the fish cards to see whether the result of the crosses described support your hypothesis. • The cards show photographs of stickleback fish that were stained with a solution that turns bones red, making them easier to see. • There are two sets of cards: the first set (16 cards) represents the F1 generation and the second set (40 cards) the F2 generation. • You will be sorting these cards according to whether the fish have pelvic spines. A stickleback with pelvic spines. The fish is shown in side(lateral) and belly (ventral) views, and the pelvic spines are indicated by the arrows. The pelvic spines are attached to the pelvic girdle. A stickleback without pelvic spines. The fish has a reduced pelvic girdle (indicated by the circles) with no pelvic spines attached to it. Sort the F1 set of cards into two separate piles: fish with pelvic spines and fish without pelvic spines. Count and record the total number of fish with each phenotype in the table below. What is the ratio of fish with pelvic spines to fish without pelvic spines in the F1 generation? * 16 0 1:0 Ratio (all sticklebacks have pelvic spines) Repeat the same procedure with the F2 set of cards. Count and record the total number of fish with each phenotype in the table below. 31 9 Which fish have no spines? 3:1 (3.4:1) Which trait is dominant? Extensions: Do these results support the hypothesis that the presence or absence of pelvic spines is controlled by a single gene? Explain using evidence. What is fitness? Tim Guilfoyle [email protected] tguilfoyle.cmswiki.wikispaces.net/ Phillip O. Berry Academy Charlotte, NC 28075 HHMI Ambassador https://www.google.com/search?noj=1&biw=1280&bih=675&tbm=isch&sa=1&q=thank+you+animated+gif&oq=thank+you+animate&gs_l=img.1.0.0l10.792396.795337.0.797226.17.14.0.3. 3.0.428.1481.3j4j1j0j1.9.0....0...1c.1.64.img..5.12.1488.L9ToXCUKAkQ#imgrc=7gim4UXsdit6LM%3A “Life moves pretty fast. If you don't stop and look around once in a while, you could miss it.” – Ferris Bueller Extension: Analyzing Additional Experimental Data (Do the results agree?) Crosses Between Several Marine and Freshwater Stickleback: The F1 Generation * Students should realize that although the numbers are different, their results are consistent with the crosses shown. In both cases, all fish in the F1 generation had pelvic spines. Extension: Analyzing Additional Experimental Data (Do the results agree?) Crosses Between F1 Generation Stickleback from the Marine x Bear Paw Lake You will notice that the phenotype ratios vary from family to family. Explain why every family does not show the same ratio. WHY?????? Further Extension: Chi Square Statistics The null statistical hypothesis for the F2 generation is that the observed outcome of 351 fish with pelvic spines and 97 fish without pelvic spines is not significantly different from the expected 3:1 ratio; any deviation from the expected 3:1 ratio likely occurred by chance alone. Total Fish Population: df = 2 − 1 = 1 Since p > 0.05, we cannot reject the null hypothesis. This result suggests that the difference between the observed and expected data is not statistically significant; this difference is thus likely to be solely due to chance. The Making of the Fittest: Film Introduction: Evolving Switches, Evolving Bodies • Freshwater stickleback populations were established when marine populations became trapped in lakes, initially connected to the ocean, that formed at the end of the last ice age. • Freshwater stickleback populations are very different from marine populations because they have adapted to life in freshwater environments. • Freshwater stickleback fish underwent many changes (color, size, skeleton) as they adapted to life in freshwater. • This activity focuses on changes in the pelvic skeleton because this trait is highly variable and is easy to see and measure. • The underlying genetic mechanisms are well studied too. The Making of the Fittest: Film Introduction: Evolving Switches, Evolving Bodies • Freshwater stickleback populations were established when marine populations became trapped in lakes, initially connected to the ocean, that formed at the end of the last ice age. • Freshwater stickleback fish underwent many “changes” (color, size, skeleton) as they adapted to life in freshwater. • This activity focuses on changes in the pelvic skeleton because this trait is highly variable and is easy to see and measure. • The underlying genetic mechanisms are well studied too. It changed your teaching and you don't know how your students learned without it? https://www.google.com/search?noj=1&biw=1280&bih=675&tbm=isch&sa=1&q=survey+says&oq=survey+says&gs_l=img.3..0l10.162937.164613.0.165169.1 1.10.0.1.1.0.145.1014.6j4.10.0....0...1c.1.64.img..0.11.1015.Wpf1gMxN3N4#imgrc=N7uiBNlx4zOu_M%3A