Key learning points

1. Some variation in phenotype is caused only by the environment and is not heritable.
2. Some variation is caused by genetic material; this can be passed on to offspring via gametes or asexual reproduction.
3. A change in the sequence of bases in an organism's DNA is called a mutation and creates a genetic variant.
4. Mutations happen at random (caused by carcinogens, or by ionising radiation, or by errors when DNA is copied).
5. Most mutations have no effect on phenotype, some influence phenotype, and a few determine phenotype.

Keywords

• Phenotype - The observable traits of an organism.

• Variation - Differences between members of the same species.

• DNA - A large chemical molecule made of nucleotides. It carries the genetic code of all living organisms.

• Mutation - A change in the nucleotide base sequence in the DNA of the genome.

• Genetic variant - A region of DNA in which the sequence of nucleotide bases has been changed.

Common misconception