HiSET Science: Mutations

Mutations

Missense mutatinos, silent mutations, and nonsense mutations
Mutations are changes in DNA sequences. Point mutations are changes in a single nucleotide in a DNA sequence. Three types of point mutations are missense, silent, and nonsense.
Missense mutations result in a codon for a different amino acid. An example is mutating TGT (Cysteine codon) to TGG (Tryptophan codon).

Silent mutations result in a codon for the same amino acid as the original sequence.
An example is mutating TGT (Cysteine codon) to TGC (a different Cysteine codon).

Nonsense mutations insert a premature stop codon, typically resulting in a non-functional protein.
An example is mutating TGT (Cysteine codon) to TGA (STOP codon).

Frameshift mutations and inversion mutations
Deletions and insertions can result in the addition of amino acids, the removal of amino acids, or cause a frameshift mutation.

A frameshift mutation changes the reading frame of the mRNA (a new group of codons will be read), resulting in the formation of a new protein product.

Mutations can also occur on the chromosomal level.
For example, an inversion is when a piece of the chromosome inverts or flips its orientation.

Germline mutations and somatic mutations
Mutations can occur in somatic (body) cells and germ cells (egg and sperm). Somatic mutations develop after conception and occur in an organism's body cells such as bone cells, liver cells, or brain cells.
Somatic mutations cannot be passed on from parent to offspring. The mutation is limited to the specific descendent of the cell in which the mutation occurred.
The mutation is not in the other body cells unless they are descendants of the originally mutated cell. Somatic mutations may cause cancer or diseases. Some somatic mutations are silent. Germline mutations are present at conception and occur in an organism's germ cells, which are only egg and sperms cells. Germline mutations may be passed on from parent to offspring. Germline mutations will be present in every cell of an offspring that inherits a germline mutation. Germline mutations may cause diseases. Some germline mutations are silent.

Mutagens
Mutagens are physical and chemical agents that cause changes or errors in DNA replication. Mutagens are external factors to an organism. Examples include ionizing radiation such as ultraviolet radiation, x-rays, and gamma radiation. Viruses and microorganisms that integrate their
DNA into host chromosomes are also mutagens. Mutagens include environmental poisons such as asbestos, coal tars, tobacco, and benzene. Alcohol and diets high in fat have been shown to be mutagenic.
Not all mutations are caused by mutagens. Spontaneous mutations can occur in DNA due to molecular decay.