Variation: measure the class sim
Measure a made-up class of 30 by lowering a height measure onto each head and sorting each record card by tongue rolling, then choose the right graph for each: a histogram whose bars touch, or a bar chart with gaps.
Variation within a species: continuous variation (height) and discontinuous variation (tongue rolling), recording results in a frequency table with tallies, and choosing a histogram for continuous data and a bar chart for discontinuous data · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Variation in a class: differences between individuals of the same species. Height is continuous variation: it can be any value within a range, so heights are grouped into classes and drawn as a histogram, whose bars touch. Tongue rolling is discontinuous variation: each person is in one of two separate groups, so it is drawn as a bar chart, with gaps between the bars. Continuous variation is usually affected by many genes and by the environment; discontinuous variation, such as ABO blood group, is usually decided by genes alone. Simplified on purpose: illustrative: a made-up class of 30 students, not real people or real measurements; the heights are in a realistic range for 15 to 16 year olds (here 148 to 182 cm); each student is measured once, standing straight without shoes, and read to the nearest cm; real readings have small errors; heights are grouped in classes of 5 cm by the recorded value (for example 160–164 cm); because heights are recorded to the nearest cm, the 145–149 class really covers 144.5 to 149.5 cm, and the bars are drawn from 145, 150 … as is usual in school; tongue rolling is shown as two clear groups; it is a common textbook example of discontinuous variation, but studies show it is not controlled by one gene alone, and some people learn to do it; the height measure on the bench is a 1 : 10 model; the close-up draws it to its own scale; the students are drawn as plain outlines.
- Lit: the headpiece, lowered onto each head
- Close-up: the height measure, the tongue and the trays, and your graphs
- Dashed outline: an empty place to drop something
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