1Variation
Variation is the differences between living things. Individuals of the same species share most of their genes, but still vary. Different species vary far more, because their genes are different.
Variation
Lesson 28.2 notes
Inheritance and variation
Variation within and between species, genes or environment, continuous and discontinuous variation, and how sex is decided.
2Species
A species is a group of organisms that can breed together to produce fertile offspring. Horses and donkeys are different species: their young, mules, can't usually breed.
species
3Genes or environment?
Some characteristics are inherited, such as blood group. Some come from the environment, such as a scar or the language you speak. Many, such as height and body mass, depend on both.
inheritedenvironment
4Identical twins
Identical twins come from one fertilised egg that split in two, so they have exactly the same genes. Any differences between them, such as in mass or fitness, come from their environment.
5Continuous variation
Continuous variation can take any value in a range, like height or hand span. Group the measurements into ranges and draw a histogram: the bars touch, and most people are near the middle.
Continuous variation
6Discontinuous variation
Discontinuous variation falls into separate groups with nothing in between, like blood group: A, B, AB or O. Draw a bar chart with gaps between the bars.
Discontinuous variation
7Boy or girl?
One pair of chromosomes decides sex: females have XX and males XY. Every egg carries an X, but a sperm carries an X or a Y, so the sperm decides.
Explore: Variation lab
Survey a class: measure heights and find blood groups, a few students at a time. Watch a hump-shaped histogram and a bar chart with gaps appear.
Common mistake: Identical twins are not exactly alike
Identical twins have the same genes, but diet and exercise make them differ in mass and fitness, and conditions in the womb give them different fingerprints. The environment matters too.
Remember
- Variation is the differences between individuals. Members of a species share most of their genes; different species have different genes.
- Some characteristics are inherited (blood group), some come from the environment (a scar), and many from both (height).
- Continuous variation can take any value in a range (height): plot a histogram. Discontinuous variation falls into groups (blood group): plot a bar chart with gaps.
Going further at GCSE