Variation

- All plants and animals have characteristics that are in some ways similar to their parents'

- This is because an organism's characteristics are determined by the genes inherited from their parents

- These genes are passed on in sex cells (gametes), from which the offspring develop

- Most animals and lots of plants get some genes from the mother and some of the father

- This combining of genes from two parents causes genetic variation - no two of the species are genetically identical

- Some characteristics are determined only by genes - in animals these include eye colour, blood group and inherited disorders (haemophilia and cystic fibrosis)

- The environment, including the conditions that organisms live and grow in, also causes differences between members of the same species - environmental variation

- A plant grown in plenty of sunlight would be luscious and green - but the same plant grown in darkness would grow tall and spindly and have yellow leaves - environmental variations

- This covers a wide range of differences

- Most characteristics (body weight, height, skin colour, condition of teeth, academic or athletic ability, etc.) are determined by a mixture of genetic and environmental factors

- For example, the maximum height that an animal or plant could grow to is determined by its genes, but whether it actually grows that tall depends on its environment

- Mutations are changes to the sequence of bases in DNA

- Mutations can lead to changes in the protein that a gene codes for

- Most mutations have no effect on the proteins that gene codes for, so most mutations have no effect on the organism's phenotype - some have a small influence on phenotype, and so only alter characteristics slightly

- It is rare that mutations can result in a new phenotype being seen in a species

- If the environment changes, and the new phenotype makes an individula more suited to the new environment, it can become common throughout the species relatively quickly by natural selection