DNA Mutation€¦ · Classes of Mutations 1. Silent: not expressed transcription and translation of the sense strand still results in a healthy protein Thursday, November 23, 17

DNA Mutation

Thursday, November 23, 17

a change in the genetic material of an organism

mutations are copied during DNA replication and passed to daughter cells

mutations in reproductive cells can be passed on from one generation to another

mutations in somatic (body) cells do not affect future generations


Causes of mutations may vary:

1. Spontaneous (randomly/by chance)

2. Sexual recombination (fertilization)

3. Gametic recombination (meiosis and cross over)

4. Environmental (chemical exposure, radiation)


Mutagens increase the rate of changes to the DNA sequence

Physical mutagen physically change the structure of DNA (eg. xrays, UVradiation)

Chemical mutagen a molecule that induces mutations by reacting chemically with the DNA (eg. cigarette smoke)


1. Beneficial: a mutation increases the adaptability and variation of a species (eg. Brain size in humans)

Mutation Outcomes


2. Neutral: the mutation has no effect due to a change in the:

a) nonsense strand this gene is not transcribed nor translated b) intron: the gene is transcribed but not translated (spliced out) c) mRNA: mutation is transcribed but results in a codon for the same amino acid

Mutation Outcomes


3. Deleterious: gene change manifests disease/death (eg.,cystic fibrosis, hemophilia, muscular dystrophy, dyslexia)

Mutation Outcomes


Classes of Mutations

1. Silent: not expressed




occurs in nonsense strand or intron region




transcription and translation of the sense strand still results in a healthy protein



2. Nonsense: is expressed

changes a healthy codon into a deleterious one, usually lethal



2. Nonsense: is expressed

often changes an amino acid codon to a stop codon eg. UAT → UAG

transcription ceases and translation does not occur, no protein is produced



3. Missense: is expressed

causes a shift in the reading frame (eg. point, deletion, insertion, inversion mutations)



3. Missense: is expressed

changes the amino acid sequence, producing a new/foreign protein transcription and translation still occur


Mutations Impact Different Levels

Single gene/point mutation (can be missense, nonsense or silent)

involves a single nitrogenous base



3 types of point mutations:

1) addition/insertion AGC GAA → AGU CGA A

Ser Glu → Ser Arg




2. Subtraction/deletion

GCA AGC UGA → GAA GCU GA Ala Ser Stop → Glu Ala




3. Substitution : wobble effect (possibly)

AGC GAA → AGU GAA Ser Glu → Ser Glu

AGC GAA → AGG GAA Ser Glu → Arg Glu



Multigene mutations

involves blocks of genes called “transposons”



Multigene mutations

1. Deletions or duplications

portion of chromosome is deleted or duplicated



Multigene mutations

2. Translocations

involves large segments at the chromosome level

a relocation of groups of base pairs from one part of the genome to another



Multigene mutations

2. Translocations

the DNA sequences that "swapped" places are called transposons



3. Inversions chromosome segments reverse orientation

no gain or loss of genetic material

involves homologous chromosomes


Documents

DNA Mutation€¦ · Classes of Mutations 1. Silent: not expressed transcription and translation of the sense strand still results in a healthy protein Thursday, November 23, 17