9.2: Stating the Hypothesis - Which Phenotype Is Dominant?
In this activity you will examine the offspring of a genetic cross between a stickleback from the ocean (marine stickleback) and a freshwater stickleback from Bear Paw Lake.
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Based on what you learned in the film, what are the phenotypes of these two parental stickleback fish?
Marine: were pelvic spines present, or were pelvic spines absent?
Bear Paw Lake: were pelvic spines present, or were pelvic spines absent? - 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?
- What is your hypothesis for which phenotype is dominant and which one is recessive?
- Based on your hypothesis, what would you expect to be the results of the cross between the marine and Bear Paw Lake stickleback parents? Make your prediction using a Punnett square.
- What would be the ratio of stickleback with pelvic spines to stickleback without spines in the first filial (F 1 ) generation?
- Using the Punnett square below, what do you expect would be the result of crossing two F 1 fish to produce the second filial (F 2 ) generation?
- What would be the ratio of stickleback with pelvic spines to stickleback without spines in the F 2 generation?
- If you had 40 offspring in the F 2 generation, approximately how many would you expect to have pelvic spines and how many to lack pelvic spines?