Genetics: Ch 18 DNA Mutation and Repair

mutation

heritable change in DNA sequence

mutation rate

frequency of mutation in a gene

somatic vs. germline mutations

somatic→ body cells

germline→ inherited

substitution

one base replaced

• transition→ same base type

• transversion→ different base type

frameshift (indel)

insertion/deletion shifts reading frame

repeat expansion

repeated sequences increase

neutral mutation

no effect

loss of function mutation

reduced/absent protein

gain of function mutation

increased/new function

lethal mutation

causes death

suppressor mutation

masks another mutation

spontaneous mutation

• replication errors

• tautomer shifts

• depurination (abasic sites)

• deamination (C→U)

induced mutation/mutagens

• base analogs (5-bromouracil)

• alkylating agents

• intercalating agents→frameshifts

• radiation (UV→thymine dimers, or Ionizing→free radicals, strand breaks)

transposable elements

mobile DNA sequences

DNA transposons

cut and paste

retrotransposons

copy and paste via RNA

transposable elements effects

can disrupt genes or cause rearrangements

homologous recombinations

accurate and use templates for DNA repair method

nonhomologous end joining (NHEJ)

error-prone DNA repair method

base excision repair (BER)

small damage DNA repair method

nucleotide excision repair (NER)

bulky damage (ex: thymine dimers) DNA repair method

mismatch repair (MMR)

replication errors DNA repair method

xeroderma pigmentosum

example of defective nucleotide excision repair (NER)

lynch syndrome

example of defective mismatch repair (MMR)