genetics chapter 18 mutations

Somatic cell mutations

All non-reproductive cells, mutations here are mostly benign; daughter cells get the mutation

Germline mutations

Occurs in gamete cells; mutations is passed to offspring

Gene mutations

Occurs in single gene; requires dna sequencing to detect mutation

Chromosome mutations

Can see under microscope, multiple genes could be affected

Base substitution (single nucleotide polymorphism)

Only one nucleotide is changed with another. Would rather get mutations in the last nucleotide of the codon

Base insertion and deletion

Shifts the reading frame and changes every amino acid after

Transversion

Purine to pyrimidine or pyrimidine to purine

• makes dna helix smaller or bigger

Transition

Purine to purine or pyrimidine to pyrimidine

• won’t change for helix size

Frame shift mutations and what are the two types of frameshift mutations.

Changes reading frame

Insertions and deletion

In frame insertion/deletion

Insertion or deletion of codons so doesn’t change reading frame

Repeated codons

Usually repetition in an area that doesn’t encode for a gene

• huntingtons disease- repeating cag for 37-121 repeats when normal is 9-37

Forward mutations

Changes normal to abnormal protein

Reverse mutation

Changes an abnormal protein to normal

Missense mutations

Mutation changes the amino acid

Nonsense mutation

End index for a stop codon

Silent mutation

Changes the nucleotide but there is an amino acid change (usually a change with the third nucleotide)

Neutral mutation

Changes the amino acid but doesn’t change protein function

• Polar protein changes to a different polar protein

Loss of function mutations

Stops the normal activity of a protein

Gain of function mutation

Produces an entirely new trait to add or amplify to the original trait

Mutation rate

Rate at which a wild type switches to a mutant allele

• dependent on the environment and organism

• Ex: exposure to UV without sunscreen will increase rate of mutation

Spontaneous mutation

Mutations that occur under normal conditions

• dna pol making mistakes in replication

Induced mutations

Environmental changes (chemical or physiological) that increase rate of mutation

Strand slippage

When one nucleotide strand during replication forms a small loop

• dna pol can’t see the loop resulting in insertion or deletion

• If template strand has loop = deletion

• If non template strand has loop = insertion

Deamination

Loss of amino group from a base

• cytosine deaminates to uracil

Mutagens

Increases mutations rate

• Ex- base analogs

Base analogs

Very similar to DNA

• 5 bromo uracil which acts like cytosine and pairs with guanine

• dna pol can’t distinguish between base analog and base

Intercalating agents

Sits in between bases and increases the distance between rungs of the ladder

• ethidium bromide

• Leads to frameshift mutations

Radiation from x rays and uv

X-rays- changes structure of bases

UV- causes thymine thymine bonding

Ionizing radiating

Causes double stranded breaks

• Rosalind franklin

First line of defence

DNA pol with its proof reading and exonuclease activity

• happens right after the wrong base is laid

Second line of defense

Mismatch repair system

Mismatch repair system

cuts non template strand bc template strand already has chemical modifications.

Goes to the nearest unmethylated site and excises all the way to the wrong nucleotide

Direct repair

Enzyme fixes the modification

Base excision

Glycosylase cuts the bind between incorrect nucleotides, dna pol adds the right base, ligase binds the two nucleotides tg

How to repair double stranded breaks?

Homologous recombination or nonhomologous end joining (nhet)

Homologous recombination

Uses info on sister chromatid

Only wires in s and g2 since that’s when sister chromtids are tg

Non homologous end joining (nhet)

Glueing tg random broken ends

• very error prone

• Normally the default pathway

• Can cause frame shifts