In this activity, students will watch a video. This will be followed by a teacher-ed discussion on the genetic control of spine development in stickleback fish. Based on the discussion, students consider which alleles for spine development are likely dominant. Students then re-watch the video but collect evidence to determine the correct response. Based on the evidence they collect, students hypothesize which allele for the spine gene is more likely to be the dominant one. Students evaluate their hypothesis by analyzing the photographic results for the F1 and F2 generation from pure breeding spine fish and from pure breeding spineless fish.