By Dean, Lisa, Nicola & Kunal Definition: a. A change of the DNA sequence within a gene or chromosome of an organism resulting in the creation of a new character or trait not found in the parental type. b. The process by which such a change occurs in a chromosome, either through an alteration in the nucleotide sequence of the DNA coding for a gene or through a change in the physical arrangement of a chromosome.
Since all cells in our body contain DNA, there are lots of places for mutations to occur. Some mutations cannot be passed on to offspring and don not matter for evolution. Somatic mutations occur in non-reproductive cells (in a single body cell) and won’t be passed onto offspring. Gametic mutations occur in the egg.
Substitution: A substitution is a mutation that exchanges one base for another. Eg, switching A to G This could: (a)change a codon to one that encodes different amino acid and causes a small change in protein produced. (b)change a codon to one that encodes the same amino acid and causes no change to protein produced. (This is called a silent mutation) OR (c)change an amino-acid-coding codon to a single ‘stop’ codon and cause an incomplete protein. This can have serious effects as an incomplete protein won’t function.
Insertion: Insertions cause mutations in which extra base pairs are inserted into a new place in the DNA. The DNA up until the insertion isn’t changed. The insertion creates a large scale frame shift resulting in a new sequence of amino acids. The resulting protein is unlikely to have any biological activity. Frame shift: A frame shift is when insertions and deletions can alter a gene so that its message is no longer correctly parsed. Eg, Consider the sentence “The fat cat sat.” Each word is a codon. If we delete the first letter and parse the sentence in the same way, it doesn’t make sense.
Deletion: Deletions are mutations in which a section of DNA is lost, or deleted. There will be a large scale frame shift resulting in a completely new sequence of amino acids. The resulting protein is unlikely to have any biological activity. Translocation: Translocation involves the movement of a group of genes between different chromosomes. A piece of one chromosome breaks off and joins onto another chromosome. This will cause major problems when the chromosomes are passed to gametes. Some will receive extra genes, while some will be deficient. Duplication: A segment is lost from one chromosome and is added to its homologue. The chromosome with the segment removed is deficient in genes. Some gametes will receive double the genes while others will have no genes for the affected segment.
Non lethal mutations accumulate within the gene pool and increase the amount of genetic variation. The abundance of some genetic changes within the gene pool can be reduced by natural selection, while other "more favourable" mutations may accumulate and result in adaptive evolutionary changes. Mutations are random occurrences which change the genome of an organism. They greatly increase genetic diversity, where advantageous mutations are favoured by natural selection and disadvantageous ones are phased out.
A mutagen is an agent of substance that can bring about permanent alteration to the physical composition of a DNA gene so that the genetic message is changed.
Chemical mutagen: This mutagen changes the base sequence in a DNA gene in the following ways: -Fails to pair the bases correctly during DNA replication, even though it mimics the correct nucleotide bases in a DNA molecule. -Adds hydrocarbon groups to nucleotides, which also causes incorrect base pairing during DNA replication Radiation: Radiation from X-rays or radioactive materials is absorbed by water molecule atoms that surround the DNA. Radiation can cause double strand breaks in DNA molecules, which cannot be repaired by the cells mechanisms. Spontaneous mutation: These mutations occur without any exposure to mutagens. DNA can sometimes shift to different chemical forms without warning (known as isomer). This causes mistakes during DNA replication.