Types Of Mutations


Mutations

  • Alternations to the usual DNA seq of an org that results from the action of chemical and physical agents or errors in DNA replication
  • They are perpetuated by cell division
  • Org may have wild type/mutant phenotype
  • Only mutations in coding region affect protein synthesis.
  • There are various ways to classify mutations:

 

  1. SPONTANEOUS V/S INDUCED MUTATION

 

Spontaneous

Induced

    • Happen naturally
    • Produce genetic variation in the population
    • Eg. Mutations occurring during enzymatic process of DNA replication
    • Result of the influence of any artificial factor.

 

 

  1. SOMATIC V/S GERMINAL MUTATION

 

Somatic

Germinal

    • Occur in DNA of somatic cells
    • Descendants of that cell will inherit the mutation and cannot pass it to germ cell
    • Such mutant cell die with individual
    • Eg cancer ( the gene regulating cell div, mutates and the cell starts dividing when it should not result into a cancerous tissue which dies with the individual and not inherited by children
    • Other eg. Delicious apples/twin apples, navel orange.

     

    • Occur in germinal cell
    • If the germ cell mutates, all the gametes produced by this cell will carry the mutated genes thus such a mutation gets passed on to the progeny.
    • Eg short legged lamb observed by a Norwegian farmer in his flock of sheep

 

  1. POINT/GENE MUTATIONS V/S CHROMOSOMAL MUTATIONS 

 


Point mutation

Chromosomal mutation

Involve a change in the base present at any position in a gene.

 

Types:6

  • Missence mutation
  • Involves the alteration of a single base which changes a codon such that the encoded amino acid is altered.
  • It is less harmful.
  • Eg.

 DNA  RNA  PROTIEN

ACA - UGU -  CysteiN

ACC - UGG - Tryptophan

 

  • Nonsense mutation
  • These mutations change a codon for an amino acid into a termination/stop codon.
  • Cause translation of mRNA to end, hence shortened protein is produced
  • Have serious effect producing a mutant phenotype
  • Eg

DNA  RNA  PROTIEN

ACA - UGU -  Cystein

ACT - UGA -  stop codon

 

  • Frame shift mutation
  • Results from insertion of extra bases or deletion of existing bases from DNA seq of genes
  • If the no of inserted/deleted isn't multiple of 3 the reading frame is altered hence different a.a is produced.
  • Serious effect with a mutant phenotype

CTC CTC CTC               CTCC CTC CTC

GAG GAG GAG            GAGG GAG GAG

Glu-glu-glu                   glu-gly-gly

 

  • Silent mutation
  • These mutation occur at 3rd base of codon and due to degeneracy of genetic code, no change.
  • No effect, not harmful

Eg CAA, CCG, CCT, CCC - glycine

 

  • Transition mutation
  • A base is replaced by another base of same chemical category purine replaced by purine

 

  • Transversion mutation
  • A base is replaced by another base of different chemical category purine replaced by purine

 

CATTCACCT

GTAAGTGGA

 

CATCCACCT

GTAGGTGGA

 

 

It involves alteration of longer DNA stretches
since these effects encoded protein, it results in mutant phenotype.
Types:2

  • Structural aberrations: shape and size of chromosome changes
  1. Deletions = involves loss or absence of a sections of chromosomes containing 1 or more genes.

Subtypes:

  1. Terminal deletions:

Involves a single break and capping of the broken end with a telomere.

A ring chromosome is formed from 2 terminal deletions. There is a break in both the long and short arm, with the fusion of ends of centromeric segment and loss of the 2 terminal seg.

 

  1. interstitial deletions:

Involves 2 breaks with loss of interstitial seg.

 

  1. Duplications = A portion of the chromosome is duplicated resulting in extra genetic material.

Subtypes:

  1. Tandem duplication:

The duplicated seg remains adj to the normal corresponding section of the chromosome.

 

  1. Reverse Tandem duplication:

Duplicated seq is in the reverse order of the normal seq.

 

  1. Displaced duplication:

The duplicated seg is loacated in the same chromosome but away from normal seg

 

  1. Transposed duplication:

The duplicated seg is located on a homolougous chromosome.

 

  1. Translocation =when portion of one chromosome is transferred to another non homologous chromosome.

Subtypes:

  1. Reciprocal translocation:

Segments of 2 different non homologous chromosomes have been exchanged

           

          2. Robertsonian translocation

  • Here, 2 heterologous acrocentric chromosome get stuck together making one large chromosome
  • A person thus has 45 chromosomes instead of 46
  • Occurs only between acrocentric chromosomes


 

  1. Inversions =a portion of the chromosome has broken off turned upside down and reattached thus genetic material is inverted.

Subtypes:

  1. Pericentric inversion:

Involvesbrea in each arm of the chromosome , 180 degree rotation of the centric seg. And reuninon of the terminal seg. With centric seg.

 

AB|C.DE|FGHI    =      ABED.CFGHI

 

  1. Paracentric inversion:

Involves 2 breakes in the same arm ,180 degree rotation f the interstitial seg and reunion of the terminal seg with interstitial seg.

 

ABC.D|EFG|HI    =     ABC.DGFEHI
 

  • Numerical aberrations: number of chromosomes is altered.

Subtypes:

  1. Polyploidy
  • Org gains or loses one or more complete set ofchromosome thus change in ploidy number.
  • Eg. Triploid (3n), tetraploid (4n) etc
  • Found in plants rare in animals

 

 

  1. Aneuploidy
  • Org gains or loses one or more chromosome and not the entire set.
  • Seen as disorder I humans eg down syndrome (trisomy 21), Klinefelter syndrome (  47, XXY), turner syndrome (45, X)
  • Eg.
  1. Trisomy (2n+1) addition of extra copy of any one chromosome.
  2. Monosomy (2n-1) deletion of one copy of any one chromosome
  3. Nullisomy (2n-2) deletion of both copies of chromosome.

 

 


  1. MUTATIONS AFFECTING MORPHOLOGICAL TRAITS
  • These mutations can be visualized phenotypically and are imp for experimental genetics
  • Eg. Various mutants of drosophila (eye color)

 

  1. MUTAIONS EXHIBITING NUTRITIONAL VARIATIONS IN PHENOTYPE
  • These have been studied in bacteria and fungi in which mutants failed to synthesize an amino acid or a vitamin

 

  1. MUTATIONS EXHIBITING BIOCHEMICAL VARIATIONS IN PHENOTYPE.
  • These mutations affect essential metabolic pathway resulting into disorders.
  • Eg. Sickle cell anemia, hemophilia

 

  1. BEHAVIORAL MUTATIONS
  • These mutations affect the behavioral patterns of an org such as mating behavior
  • Eg. Mating behavior of a fruit fly maybe impaired if it cannot beat its wings

 

  1. LETHAL MUTATIONS
  • These mutations interrupt the processes that are essential to the survival of the org.
  • Eg a mutant bacterium that cannot synthesize a specific amino acid it needs will be unable to grow and divide if plated in a medium lacking that amino acid.
  • Other eg. Tay-Sachs diseases and Huntington's diseases in Human.



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