A mutation is a change in a DNA base-pair or region of chromosome, of which there are many causes :A somatic mutation affects the individual in which it happens and is not passed on to the succeeding generationGerm-line mutations may be transmitted by the gametes to the next generation, producing an individual with mutations in both the somatic and germ-line cellsGerm-line mutations are heritable.

Mutations can occur spontaneously or be induced by a mutagen, which is a chemical or physical agent that increases the frequency of mutational events.Not all mutations are caused by mutagens: so-called "spontaneous mutations" occur due to spontaneous hydrolysis, errors in DNA replication, repair and recombination.

A chromosomal mutation or aberration is a change in the structure or number of chromosomes.A gene mutation is a change in the DNA sequence of a particular gene.

A point-mutation is a base-pair substitution mutation, in which one base pair is replaced by another base pair (AT to GC).

And A point-mutation include :

Transition mutations, in which the change is from one purine-pyrimidine base pair to the other purine-pyrimidine base pair (AT to GC, GC to AT, TA to CG, and CG to TA) .Transitions can be caused by oxidative deamination.

Transversion mutations involve a change from a purine-pyrimidine base pair to a pyrimidine-purine base pair (AT to TA, GC to CG, AT to CG, and GC to TA)Transversions can be caused by ionizing radiation.

Types of Mutations

Genetic mutationsby : asem shadid

Types of Mutations according to their effects on amino acid sequences in proteins :

• Missense mutations, a gene mutation in which a change in the DNA causes a change in an mRNA codon so that a different amino acid is inserted into a polypeptide during biosynthesis.

In sickle-cell anemia: a single nucleotide base-pair change in codon 6 of the -hemoglobin gene leads to an amino acid substitution in the -hemoglobin chain.

• Nonsense mutations, in which an mRNA codon is changed from an amino acid into a stop codon (UAG, UAA, or UGA).

• Neutral mutations, which produce no detectable change in the function of the protein translated from the message.

It is a subset of missense mutations where the new codon codes for a different amino acid which is chemically equivalent to the original one i.e Lys to Arg (protein function is not affected).

• Silent mutations are mutations in which a base pair change transforms a codon into another codon for the same amino acid, with no detectable change in the resulting protein.

• Frameshift mutations, which result when the reading frame of a gene is shifted due to the addition or deletion of one or two more base pairs in a gene .It results in a non-functional protein.

Point mutations are of two classes: Forward mutations Reverse mutations

Forward mutations cause the genotype to change from wild-type to mutant

A reversion is a mutational event that changes a mutant phenotype back to wild-type

A suppressor mutation is a mutation at a different site from an original mutation that does not result in a reversal of the original mutation but instead masks or compensates for the effects of the initial mutation .suppressor mutation (secondary or second site mutation)

There are two major classes of suppressor mutations:

1. Intragenic suppressors occur within the same mutated gene

2. Intergenic suppressors occur in different genes

Types of Base-Pair Substitution Mutations