13.1Chapter 13: Variation and Natural Selection

Variation in animals and plants — Alhussan Biology - Stage 9 Revision Notes & Topical Questions

5 min read 10 parts Lesson 1 of 8 2 quizzes

📚 Alhussan Biology - Stage 9 Hub / Topical Revision

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Lesson summary

13.1 Variation in animals and plants — Genetic and Environmental Variation — Alhussan International Academy — Biology (Stages 7–9) notes: Distinguish genetic from environmental variation and continuous from discontinuous variation, and explain how variation arises and why it matt…

Between species
Within a species
Easy to see
Hard to see
Blood groups
Adaptation

Part 1 of 8What variation is

Variation

Variation the differences between individuals of the same species or between species.

No two individuals are exactly alike, except identical twins and clones.

Between species

Between species a palm tree and a sunflower have a lot of genetic variation between them.

Within a species

Within a species animals share many genetic characteristics, which is why they breed successfully, but also differ from parents, siblings and cousins.

Causes

Causes variation may result from genetic differences, environmental differences or an interaction of the two.

Part 2 of 8Variation in animals

Easy to see

Easy to see some horses have longer legs than others and some butterflies have longer tongues.
Puffins differ in the colour of their feet and in the shape and pattern of the beak, which lets us identify each bird.

Hard to see

Hard to see it can involve characteristics that appear only some of the time or systems inside the animal.
Some frogs call louder than others in the breeding season.
Some people have lower blood pressure than others.

Part 3 of 8Human blood groups

Blood groups
- A, B, AB and O are inherited genetic variation and stay the same throughout life.
- Nothing in the environment changes the group.
- The right blood type is essential for a transfusion, because the wrong blood group makes the patient very ill.

Part 4 of 8Variation in plants

1Fruit

Fruit olive trees produce olives and date palms dates, but the fruit of some trees is bigger, sweeter and tastier even in the same conditions.

2Flowers

Flowers all flowers of a species, such as early spider orchids, have the same basic shape and pattern but with variation.

3Adaptation

Adaptation shared features show how the species is adapted to its environment.
Differences show the variation that lets the species adapt when the environment changes.

Part 5 of 8Genetic variation

Genetic variation

Genetic variation variation caused by differences in the genes that individuals inherit.

Sources

Sources meiosis shuffles the chromosomes so that each gamete is different, fertilisation is random and mutations create new alleles.

Examples

Examples human blood group, eye colour and tongue rolling, and plant flower colour and seed shape.

Part 6 of 8Environmental variation

Environmental variation

Environmental variation variation caused by conditions during life.

A plant grown in shade is taller and paler than the same type grown in full sun.
A person who exercises has more muscle, and a poor diet may make a person smaller.
Scars, language and tanned skin are environmental.

Both together

Both together height and mass depend on genes and environment, since good nutrition is needed to reach inherited height potential.

Identical twins

Identical twins those raised in different places show how the environment alters genetically identical individuals.

Part 7 of 8Continuous and discontinuous variation

Type	Description	Example	Graph
Continuous	Any value in a range; many genes and environment	Height, mass, leaf length	Bell-shaped histogram
Discontinuous	Distinct groups with no in-betweens; mostly genes	Blood group, tongue rolling	Bar chart

Investigating
- measure a characteristic in a large sample, such as the length of 50 leaves, group the data into classes and draw a histogram.
- A normal distribution has most values near the mean and few at the extremes.
- Summarise results by the mean and the range, using the same measuring method.

Part 8 of 8Why variation matters

Natural selection

Natural selection variation allows it to occur.
If all individuals were identical, a change such as a new disease could kill the whole population.

Selective breeding

Selective breeding farmers and breeders use variation to choose animals or plants with the best features.

Key terms

Term	Meaning
Variation	Differences between individuals of a species.
Genetic variation	Variation caused by inherited genes.
Environmental variation	Variation caused by conditions during life.
Continuous variation	Variation with a range of values between extremes.
Discontinuous variation	Variation in distinct groups with no in-betweens.
Mutation	A random change in a gene.