Laboratory work 8: studying statistical regularities of modification variation
When a trait (for example length) is measured in many objects of one species, variety or plant (say 100 bean seeds or leaves), the values are not all the same; written in increasing order they form a variation series. Each value is a variant (v) and the number of times it occurs is its frequency (p). The mean value is M = (v₁p₁ + v₂p₂ + …) ÷ n, where n is the total number of objects. Showing the frequencies in a bar diagram and joining the tops gives the variation curve: it is bell-shaped, with average values most common and very small and very large values rare. This is the statistical pattern of modification variation: many chance environmental factors act, and the values stay within the norm of reaction. In the work do not put seeds or leaves in your mouth, measure carefully with a ruler and record the results in a table.
“The variation curve”. Measure the length in mm of 30–50 leaves (picked with permission, one species), make a table, draw the frequencies as bars and find M.