The origin of genetic variation
I Motivation
Evolution is a change in the genotype of the population over time. Phenotypic differences
between species reflects genetic differences between species = genetic variation across species
What is the origin of genetic variation??
Ultimate:MUTATION!!!!!!!!!!!!!!!!!!!!!!!!!!!!
II. What is a mutation???
-new variant of DNA that is different from both parents
-deleterious alleles in population are often referred to as mutations
Variation at third position is much greater than at other two
Transitions are more common than transversions because DNA
DNA repair enzymes can recognize wrong insertion representing a
a transition better than a transversion
III. Properties of Mutations
Random
Rates: high, about 1 new mutation per gamete
Effect: deleterious? and generally weak
IV. Origin of new loci/function: Gene Duplication
Occurs through unequal crossing over
Paralogs- loci that are duplicated and then diverge
Orthologs- loci that are homologous then diverge
Pseudogenes- clase of genes that have no function
V. Chromosome inversions
Suppress recombination and perhaps preserve multilocus based adaptations
VI. Polyploidy
duplication of the basic number of chromosomes,
e.g.: 2n to 3 n to 4n etc.,
can lead to instant speciation through reproductive isolation
VII. Much variation in populations
Heterozygosity: average frequency of heterozygotes across loci
Proportion of loci polymorphic
Lots of genetic variation within natural populations
What maintains it?
VIII. Conclusion
Mutation rates are high
Mutations effect fitness
Mutations contribute to genetic variation
Duplications can lead to new gene function
Polyploidy can lead to instant speciation
Inversions can protect adaptations
Mutations are important to evolution