Types of Base-Pair Substitution Mutations Genetic mutations and Type of mutation done by : asem shadid , college of medicine .

1. 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 generation
Germ-line mutations may be transmitted by the gametes to the next generation,
producing an individual with mutations in both the somatic and germ-line cells
Germ-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 mutations
by : asem shadid

2. 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.

3. 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

4. Types of Base-Pair Substitution Mutations