Transcript lecture12
Mutation & genetic variation Mutations Mutations gene – stretch of dna that codes for a distinctive type of rna or protein allele – versions of the same gene that differ in their base sequence mutation – any change in the base sequence of dna Types of mutations Point mutation Frameshift mutation Gene duplication Chromosome inversion Polyploidy Point mutation Point mutations are single base substitutions in DNA Point mutation Genetic code Frameshift mutation Frameshift mutation Gene duplication Gene duplication Duplicated loci can: -retain their original function and provide an additional copy of the parent locus -gain a new function through mutation & selection -become functionless pseudogenes Chromosome inversion Chromosome inversion Inversions change gene order and decrease the frequency of crossing over As a result, the alleles inside the inversion tend to be inherited as a unit Polyploidy Polyploidy Polyploid populations are reproductively isolated from their parental species Fitness effects of mutation Mutation rate Species Taxon mutations/genome/ generation E. coli bacteria S. acidocaldarius archaea S. cerevisiae fungi 0.0025 0.0018 0.0027 C. elegans D. melanogaster M. musculus H. sapiens 0.0360 0.1400 0.9000 1.6000 roundworm insect mammal mammal Mutation rate Mutation rates vary among species because of differences in the number of cell divisions that take place prior to gamete formation Human Fruit fly 400 cell divisions 25 cell divisions Polymorphism If more than one allele exists at a particular locus, a population is said to be polymorphic at that locus Polymorphism One third to one half of all coding loci are polymorphic in a typical population Why are populations genetically diverse? Selectionist theory - genetic diversity maintained by natural selection Neutral theory - genetic diversity maintained because it is not eliminated by selection