19.1 mutations and variations

what is a mutation

a change in the base sequences of DNA

what are the different types of mutation

substitution, deletion, insertion

point mutation

if only one nucleotide is affected

why is the degenerate nature of genetic code important

the new codon after a mutation may still code for the same amino acid leading to no change in the protein synthesised

how does a substitution mutation affect a protein

• changes the codon in which it occurs

• if the new codon codes for a different amino acid, this will lead to a change in the primary structure of the protein

frameshift mutation

• the insertion or deletion of a nucleotide or nucleotides

• the reading frame for the sequence of bases is shifted

• this will change every successive codon form the point of mutation

possible affects of a mutation

no effect - normally functioning proteins are still synthesised

damaging - proteins are either no longer synthesises or proteins which are synthesised are no longer functional

benenficial - results in new and useful characteristics in the phenotype

words for loss of purine base

depurination

loss of a pyrimadine base

depyramidination

what is a mutagen

chemical, physical or biological agent which causes mutations

physical mutagens

ionizing radiations such as x rays

can break one or both DNA strands - some breaks can be repaired but mutations can occur in the process

chemical mutagens

deaminating agents

chemically alter bases in DNA such as converting cytosine to uracil in DNA, changing the base sequence

biological agents - alkyating agents

methyl or ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication

biological agents - base analogs

incorporated into DNA in place of the usual base during replication, changing the base sequence

biological agents - viruses

viral DNA may insert itself into a genome, changing the base sequence

examples of changes in chromosome structure

deletion - a section of chromosomes breaks off and is lost within the cell

duplication - sections get duplicated on a chromosome

translocation - a section of one chromosome breaks off and join another non - homologous chromosome

invertion - a section of chromosome breaks off, is reversed, and then join back onto the chromosome