14.1: How Does Mutation Arise

mutations

are changes in the nucleotide sequence of an organism's DNA, which can lead to alterations in genes and potentially affect an organism's traits.

allele

variant forms of a gene that arise through mutation

genotype

is the genetic constitution of an individual, representing the specific alleles inherited from parents.

phenotype

the observable physical or biochemical characteristics of an organism determined by its genotype.

spontaneous mutations

occur without outside influence

• through deamination - removal of amino group from nucleotide

• through transposon - DNA elements that can move from one position in genome to another = if move and land in a gene could cause functional problems with encoded gene

induced mutation

occur when some agent from outside of cell (mutagen) causes changes in DNA leading to mutation

• certain chemicals can alter nucleotide bases or add groups to bases

• radiation - 2 ways

  • X-rays and gamma produce free radicals that change bases so unrecognisable to DNA polymerase

  • UV - absorbed by T = forms covalent bonds with adjacent T = blocks DNA replication

somatic mutations

occurs in somatic cells and passed on to daughter cells during mitosis but not passed onto sexually produced offspring

germ line mutations

occurs in germ line cells which give rise to gametes and is passed to offspring at fertilisation and offspring will have mutation in every cell

2 types of mutations that affects phenotypes

loss of function and gain of function

benefits of double stranded helix in terms of mutations

contains 2 separate copies of genetic information = when one strand is damaged the complementary strand can be used as a template to restore the correct nucleotide sequence

3 common repair mechanisms

• Base excision repair focuses on fixing endogenous DNA damage such as hydrolytic damage resulting in deamination or depurination

• Nucleotide excision repair can fix damage caused by ultraviolet light or certain chemical carcinogens

• Mismatch repair fixes faulty base incorporation by DNA polymerase during replication which leads to incorrect base pairing

how can mutations be beneficial

provide genetic diversity making natural selection possible = causes phenotype to be more advantageous if environment changes