6.1.1 gene mutations Flashcards
what is a gene mutation
change to DNA
what are somatic mutations
mutations associated with mitotic division & not passed to offspring (eg. cancerous tumours)
what are the 2 main classes of DNA mutation
- point mutation = one base pair substituted for another
- insertion or deletion (indel) mutation = 1+ nucleotides inserted/deleted from length of DNA, causing a frame shift
3 types of point mutation
- silent
- missense
- nonsense
what reduces the effect of point mutations
degenerate nature of genetic code
define silent mutations
= point mutation involving change to base triplet, where triplet codes for same amino acid
- primary structure of protein not altered
- thus, neither is secondary or tertiary structure
define missense mutations
= change to base triplet sequence which leads to change in amino acid sequence of protein
- may have significant effect on protein
- alteration to primary structure leads to change in tertiary structure of protein = alters shape & prevents it from functioning normally
example of condition caused by missense mutation
- sickle cell anaemia
- missense mutation on 6th base triplet of gene for beta-polypeptide chains of haemoglobin
define nonsense mutations
= point mutation may alter base triplet, so it becomes a stop triplet
- results in truncated protein that doesn’t function
- most likely degrade within cell
2 types of indel mutations
- insertions
- deletions
= cause frameshift
describe insertion & deletion mutations
- nucleotide base pairs (not triplets) inserted in gene or deleted
- all subsequent base triplets are altered = frameshift
- when mRNA translated, the amino acid sequence after frameshift is disrupted
- primary sequence (and thus, tertiary sequence) is altered
- protein cannot carry out regular function
how have mutations been beneficial
- helped drive evolution through natural selection
- different alleles of genes produced through mutations
describe the mutation of blue eyes & how it is beneficial
- harmful in areas where sunlight intensity is high, as lack of iris pigmentation could lead to les cataracts
- beneficial in more temperature zones as enables people to see better in lower light intensity
why are different skin tones beneficial
- in africa, early humans had black skin as the high concentrations of melanin protected them from sunburn & cancer
- when humans migrated to more temperatures zones, paler skin was an advantage as it enabled vitamin D to be made in lower light intensities
- in these areas, those with paler skin would be selected, as vitamin D protects us from rickets, heart disease & cancer
examples of neutral mutations (neither beneficial or harmful)
- inability to smell certain flowers eg. freesia, honeysuckle
- differently shaped earlobes
