Factors of evolution. Laboratory work 3

The aim of the laboratory work is to find the similarities and differences among individuals of one species and study their causes. Material: wheat ears or leaves of one plant species (herbarium) prepared by the teacher, a ruler and a notebook; do not use scissors or sharp objects. Procedure: 1) number 20–30 specimens; 2) count or measure one trait in each (for example, the number of spikelets per ear or leaf length); 3) build a variation series – write the values in increasing order; 4) count how many times each value occurs (its frequency) and make a table; 5) find the mean (sum of all values : number of specimens) and the most frequent value (mode); 6) draw a bar chart in the notebook – most values cluster around the mean and few lie at the two ends (a bell-shaped curve). Conclusion: individuals of one species are both alike and different. Differences have two causes: environmental influence (modification, not inherited, within the norm of reaction) and hereditary variation (mutational, combinative). Hereditary differences are material for selection, which is why variation is important for evolution.