Variations in Populations
| English | Chinese | Pinyin |
|---|---|---|
| continuous variation | 连续变异 | lián xù biàn yì |
| discontinuous variation | 不连续变异 | bù lián xù biàn yì |
No two the same
- Look at any group of the same species and you see differences.
- People differ in height, blood group, eye colour, and much more.
- These differences within a population are its variation.
- And variation comes in two distinct patterns.
Continuous variation
- Continuous variation 连续变异 covers a smooth range of values.
- Height and body mass are examples — every value in between is possible.
- Plotted on a graph, it forms a smooth bell-shaped spread.
- This kind usually comes from many genes together, plus the environment.
Continuous variation describes a trait that…
Continuous variation covers a smooth range of values, like height or mass — usually many genes plus environment.
Discontinuous variation
- Discontinuous variation 不连续变异 falls into distinct categories.
- Blood group is A, B, AB, or O — nothing in between.
- Whether you can roll your tongue is a yes-or-no trait.
- This kind is usually controlled by just one or a few genes.
Discontinuous variation describes a trait that…
Discontinuous variation falls into clear categories, like blood group — usually one or a few genes.
Why variation matters
- Variation is the raw material that natural selection acts on.
- If every individual were identical, selection could not favour any of them.
- Genetic variation can be passed on; environmental differences cannot.
- So heritable variation is what lets populations evolve.
Continuous or discontinuous?
Sort each trait by whether it varies over a smooth range or falls into distinct categories.
Continuous variation is usually caused by many genes together, plus the environment.
Many genes adding up (polygenic) plus environmental effects give a smooth range — continuous variation.
Variation within a population is the raw material that natural ____ acts on.
Without variation, natural selection would have no differences to favour.
Select all true statements about variation.
Much variation is genetic, not just environmental. The other three are correct.
The two patterns have different causes. Continuous variation comes from many genes adding up, strongly shaped by the environment. Discontinuous variation comes from one or a few genes and is barely affected by the environment. Match the pattern to its cause.
Height versus blood group:
- Height is continuous: people range smoothly from short to tall, shaped by many genes and by nutrition.
- Blood group is discontinuous: you are exactly A, B, AB, or O, set by a single gene.
- Same person, two completely different patterns of variation.
Variation within a population comes in two patterns. Continuous variation is a smooth range (like height), caused by many genes plus the environment. Discontinuous variation falls into distinct categories (like blood group), controlled by one or a few genes. Heritable variation is the raw material for natural selection.