Students in Michelle Stuart’s Biology classes at Frenship High School recently participated in a four-day genetics lab studying the inheritance of a specific trait coded for by a singular gene. During the lab, they were asked to look at plant structures of the seedling under a stereo microscope and identify all the parts.
The experiment is a great way to bring the Punnett Square to life by using plants that the students plant themselves. The Punnett square is a diagram used to predict the outcome of a particular cross or breeding experiment. Biologists use it to determine the probability of an offspring having a particular genotype.
Students first looked at the stem color (either purple or green). This is called the phenotype or physical appearance determined by an allele. Students germinated seeds from three generations. They were able to see the action of the dominant allele in the second generation when a homozygous recessive (rr) parent is crossed with a homozygous dominant (RR) parent. The offspring were purple, and the students were able to see the result of a dominant allele in a laboratory setting.
Students then looked at a third generation that is a cross of two plant that are from the second generation. This allowed them to see the 3:1 ratio that they have been seeing on Punnett Squares in a very tangible and understandable format. Finally, students analyzed the actual experimental data and compared it to the expected results as predicted by the Punnett Square.