Population and Evolutionary Genetics Flashcards
Theory of Evolution (Darwin)
- Overproduction: every species tends to produce more individuals than can survive to maturity
- Variation: the individuals of a population have many characteristics that differ
- Selection: some individuals survive longer and reproduce more than others do
- Adaptation: the traits of those individuals that survive and reproduce will become more common in a population
Natural Selection
- trait is favoured so survival increases for that trait
Why is variation important?
- because the environment changes
- the more variation within a species, the more likely it will survive
- the more variation of types of species in a habitat, the more likely at least some will survive
Fitness
- individuals have variation in phenotype
- many of these are inherited
- individuals with particular phenotypes will survive to reproduce and pass genes to offspring
- Fitness is the relative reproductive success of a genotype
- Fitness (W) ranges from 0-1
W = N offspring produced by genotype/N offspring produced by most prolific genotype
Natural Selection can be…
- Directional
- phenotypes at one or the other end of the spectrum are selected against
- an extreme trait is selected for - shifting population toward homozygosity and phenotypes toward one extreme
- Stabilising
- natural selection favours an intermediate phenotype (heterozygote advantage - higher fitness) than extremes of traits
- reduces phenotypic variation
- Disruptive
- selection favours extreme phenotypes over any intermediate phenotype
- bimodal distribution
Sexual Selection
- selection arising through preference by one sex for certain characteristics in individuals of the other sex
- sexual dimorphism between sexes
- demonstrate fitness
- higher reproductive success
Natural vs. Sexual Selection
- Natural Selection: traits become more or less common depending on an individuals ability to survive and gather resources
- Sexual Selection: traits become more or less common depending on an individual’s ability to mate with more or better partners
Put this all together
Gene flow + Genetic drift + Mutation > Selection > Diversity
Applications of population genetics
Helps us understand genetic relationships and history
- management
- captive breeding, translocations
- anthropogenic habitat change
- landscape variability
- conservation
- individual identification
Subspecies
- genetically and/or phenotypically distinct
- able to interbred but often do not due to geographic isolation
Speciation
- Cichlids in Lake Malawi
- Finches of the Galapagos
- Nearly 1/4 of all described species are beetles
Evolutionary Genetics
- phylogenetic tree
Cladogenesis = the splitting of one lineage into two
Anagenesis = evolution within a lineage with the passage of time
Morphospecies Concept
similar in appearance
Biological Species Concept
- a population or group of populations whose members can interbreed in nature and produce viable, fertile offspring
Issues
- many species are asexual and do not mate
- not applicable to fossils
difficult to test if potential species don’t have chance to interbreed naturally
- ability to intermate sometimes drops off gradually
Pre-zygotic barrier
- gametes from different species are prevented from fusing
- incompatible gametes
- different habitats
- individuals cannot meet
- mechanical
Post-zygotic barrier
- gametes can fuse, but cannot reproduce
- hybrid
- zygote does not survive
- hybrid is sterile - mule
- F1 are viable, F2 are sterile
Phylogenetic Species Concept
Species are the smallest monophyletic groups and share an exclusive common ancestor
Speciation
Allopatric speciation
- split by geographic barrier
- gene flow is blocked
Sympatric speciation
- no geographic barrier
What is a species?
- a name given to a type of organism
- an evolutionary independent group of organisms
- sometimes the difference is clear
The biological species concept
- first developed by ernst mayr
- group of organisms that can interbreed - exchange genes
- reproductively isolated from other species - evolve independantly
Recognition Species Concept
- a species is a set of organisms that can recognize each other as potential mates
- they do not necessarily have to be able to mate
Phenetic species concept
- a species is a set of organisms that are phenotypically similar and that look different from other sets of organisms
- phenotypic similarly is all that matters in recognizing sperate species
Phylogenetic species concept
- a species is a “tip” on a phylogeny, that is, the smallest set of organisms that share an ancestor and can be distinguished from other such sets
Phylogenetic tree
- evolutionary relationship between organisms
- nodes
- branches
- rooted with ‘outgroup’
mtDNA
- 1000-10,000 “identical” copies per cell
- maternally inherited
- advantages
- inherited without recombination - phylogenetic reconstruction easier
- high mutation rate - some taxa show lower mutation rate
- analysis from “old” and “bad” samples: “ancient samples”, hairs
- Disadvantages
- information only about female history
Mutation rates generally low
Nonsynonymous changes - change amino acids
- missense, nonsense
Synonymous changes - do not change amino acids
- silent
Substitution rates - different parts of a gene
- evolution occurs at different pace in different regions of the gene
How quickly does evolution happen?
- rate of synonymous change higher than non-synonymous change
- why?
- non-synonymous change alters proteins
- may be detrimental to fitness
- most eliminated by natural selection
