Variation exists between all individuals
Two types of variation..
Intraspecific - differences that occur within a species.
Interspecific - variation between different species.
a way to remember the difference.. int-er-specific means diff-er-ent species!
All members of a species have the same genes.
However, individuals within that species may have different versions of the genes - alleles.
alleles make up an organisms genotype.
different genotypes result in variation in phenotype - the characteristics being displayed.
You inherit genes from your parents, so genetic variation is inherited.
The appearance (phenotype) of an individual is also affected by the environment.. e.g.
Plant growth - affected by the amount of minerals available in soil.
Fur colour - affected by the temperature of an animals habitat.
Identical twins - may be affected by different illnesses or growing up in different areas.
It's a combination
Variation is often a combination of genetic and environmental factors.. e.g.
A person may have the genes to grow six foot tall, but whether they do will depend on environmental factors such as diet and health.
Good luck on your exams!