DNA mutations (7.5)

susceptibility locus

specific location in the genome that increases likelihood of disease

single nucleotide polymorphisms

• one base pair variation in DNA, common

• found in non-coding regions of DNA

categories of small-scale mutations

• substitution - one base swapped for another

• insertion - one or more bases added

• deletion - one or more bases removed

• inversion - adjacent bases are flipped in orientation

categories of point mutations

• missense

• nonsense

• silent

• frameshift

missense mutation

• single base change replaces one amino acid with another

• some are harmless and some cause diseases like sickle cell anemia

nonsense mutation

• mutation changes a codon to a stop codon

• protein is cut short and likely is non-functional

• common in genetic disorders like cystic fibrosis

silent mutation

• base change that still codes for the same amino acid (change in last letter)

• no change in protein function or structure

• may affect gene expression or splicing

frameshift mutation

• caused by insertions or deletions not in a multiple of 3

• alters entire amino acid sequence

categories of large-scale mutations

• amplification

• deletion

• translocation

• inversion

• trinucleotide repeat expansion

amplification

• extra copies of a gene are created

• cab lead to overexpression or development of new traits

• role in cancer and gene evolution

translocation

• gene segment moved to a different choromosome

• unexpected effects like cancer

inversion

• DNA segment is reversed end to end within a chromosome instead of all down

• can affect function unless in non-coding regions

trinucleotide repeat expansion

• short DNA sequence is repeated more times than normal

• across generations, repeats may increase

causes of mutations

• spontaneous - mistakes during DNA replication that are not repaired

• induced - external mutagens (chemicals, radiation)

C. elegans

doubles lifespan by affecting insulin