A mutation is a change in genetic material which occurs unpredictably and produces a different allele. A mutation can also occur due to a chromosomal change, for example structurally or numerically. This can be due to carcinogens or radiation, factors known as mutagens.

Gene mutations can occur due to:

• base addition: one or more bases are added to a sequence, for example GAG CCT GAG turns into GAG CCT GAG C
• base substitution: one base is replaced by another, for example GAG CCT GAG turns into GAG CCT GTG
• base deletion: one or more bases are deleted, for example GAG CCT GAG turns into GAG CCT GA

Addition and deletion tend to have particularly bad effects because the code for that polypeptide has been broken. This leads to a frame shift in the sequence which will lead to the whole line of bases being affected.

Base substitutions, on the other hand, sometimes don’t have any effect, unless it creates a STOP triplet. Mutations that have no effect are known as silent mutations. Examples of diseases due to base substitution include sickle cell anaemia and phenylketonuria.

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Prokaryotes and Eukaryotes

Both prokaryotes and eukaryotes contain DNA however the former have no nuclei while the latter does. The purpose of the nucleus is to enclose the DNA production within one section of the cell thereby increasing efficiency. This is not necessary in prokaryote cells due to the fact that they’re so much smaller in size which means all the cell’s materials are in close proximity to each other.

Another difference between their DNA is that eukaryotic DNA is linear whereas DNA in prokaryotes is circular. While the former contains chromosomes the latter contains only one circular DNA molecule and a number of smaller DNA circlets called plasmids. Basically, the prokaryotic cell doesn’t need as many genes.