Lecture 13 Mutation and DNA Repair

mutation

change in DNA sequence

small mutation

single base pair change affecting one gene

large mutation

change to an entire chromosome that will affect many genes

Germline mutation

DNA change in a germ cell

Somatic mutation

DNA change in a somatic or body cell

Germline mutation

will be passed to offspring and present in all of their cells

Somatic mutation

may cause a phenotype in that cell or its
progeny and is not passed on to offspring

Conditional Gene Expression

effect of the mutation is dependent on other variables, such as environment, sex, diet or the presence of other mutations

Unconditional Gene Expression

mutation has its effect under all circumstances

loss of function

abolishes gene activity or protein function

reduction of function

reduces gene activity or protein function

gain of function

causes abnormal gene expression or protein function

gain of function

lead to dominant phenotypes because one copy of the mutant gene is enough to cause phenotype

reduction of function and loss of function

lead to recessive phenotypes because there are two
copies of every gene, and one copy can usually provide enough
protein to perform the function

base substitution (point mutation)

change of one base for another

transition

pyrimidine for pyrimidine (C <-> T)
purine for purine (G <-> A)

transversion

pyrimidine for purine (C or T → G or A)
purine for pyrimidine (G or A → C or T)