Inheritance, Variation & Evolution

• DNA stands for deoxyribonucleic acid. Its the chemical that all of the genetic material in a cell is made up from.
• DNA is a polymer. It's made up of two strands coiled together in the shape of a double helix.
• A gene is a small section of DNA found on a chromosome.
• Genome is the term for the entire set of genetic material in an organism.
• DNA strands are polymers made up of lots of repeating units called nucleotides. Each nucleotide consists of a sugar, a phosphate and a base.
• There are 4 bases: A, T, C, G.

  A always pairs with T, and C always pairs with G- This is called complimentary base pairing.
• Each amino acid is coded for by a sequence of three bases in the gene. The amino acids are joined together to make various proteins, depending on the order of the gene's bases.
• There are parts of DNA that don't code for proteins. Some of these non-coding parts switch genes on and off, so they control whether or not a gene is expressed.
• Proteins are made in the cell cytoplasm on ribosomes.
• To make proteins, ribosomes use the code in the DNA. DNA is found in the cell nucleus and can't move out of it because it's really big. So the cell needs to get the code from the DNA to the ribosome. This is done using a molecule called mRNA- which is made by copying the code from DNA. The mRNA acts as a messenger between the DNA and the ribosome- it carries the code between the two. The correct amino acids are brought to the ribosomes in the correct order by carrier molecules.
• A mutation is a random change in an organism's DNA. They can sometimes be inherited.
• Mutations occur continuously. They can occur spontaneously. However, the chance of mutation is increased by exposure to certain substances or some types of radiation.
• Mutations change the sequence of the DNA bases in a gene, which produces a genetic variant. As the sequence of DNA bases codes for the sequence of amino acids that make up a protein , mutations to a gene sometimes lead to changes in the protein that it codes for.
• Insertions are where a new base is inserted into the DNA base sequence where it shouldn't be. An insertion changes the way the groups of three bases are 'read', which can change the amino acids that they code for. Insertions can change more than one amino acid as they have a knock-on effect on the bases further on in the sequence.
• Deletions are when a random base is deleted from the DNA base sequence. Like insertions, they change the way that the base sequence is 'read' and have knock-on effects further down the sequence.
• Substitution mutations are when a random base in the DNA base sequence is changed to a different base.