Theme 4C (Part 1, Ways of Change) Flashcards
Genetic Drift
- Random Processes - Can affect the f of genetic variants and traits during life cycle, especially mating & survival
- Evolution by random change
- Random if probability of occurence isn’t affect by individuals phenotype
- Change in allele f due to chance in finite populations, especially small ones
Effect of Genetic Drift
- Evolution in finite populations
- Random sampling error, error higher in smaller pop
- Jelly Bean / M&M example
Fixation
- Stable, permanent in reference to an alleles presence
Bottleneck
Genetic drift reduces genetic variation in a pop
- Temporary reduction in pop size cause drift, reduce genetic variation, & cause genetic difs b/w pops - significant conservation implications
Founder Effect
Genetic drift reduces genetic variation in a pop
- Small founding pop, less diversity results in following gens
Phylogeny
- Human pops closely related to neighbours
Founder events in Human History
- Based off of path out of Africa, more heterozygosity (genetic diversity) in African individuals
- Least in Americas
- All non-Africans descend from a small pop of humans who lived in Ethiopia
Population Divergence
- Pop who over time changes distribution to homozygous on opposite ends
- Over long period of time, allele fixation occurs and populations diverge as they are now distinct from one another
Non-random Mating
- Mating individuals are more closely related or less closely related than those drawn by chance from a random mating pop
- 3 types
Interbreeding
- Mating with Relatives (Mating system)
- Caused by small pops
- Doesn’t alter allele f by itself
Ex. Self crosses with plants that can have male + female gametes
Outbreeding
Mating with individuals more distantly related (non-relative)
Assortative mating
- Individuals with similar genotypes and/or phenotypes mate with one another more frequently than would be expected under random mating pattern
- Blue frogs mostly mating with other blue frogs and not red
Inbreeding Depression
- Rare deleterious alleles more likely to combine in homozygotes
- More offspring with poorer fitness
I.e. Cystic fibrosis carriers inbreeding, making it more likely
Often in bottleneck or founder pops
Natural Selection
- Predictable change in f distribution of a trait b/w the parental & offspring gens at a result of 3 conditions
- Individuals vary
- Survival and reproduction not random
- Inheritance
Galapagos finches, big seeds vs small seed beaks
Three patterns of natural selection
Directional Selection
- Individuals of one extreme phenotype favoured
- Evolution of the trait mean occurs when fitness varies +’vely or -‘vely with “trait” size
Peppered moth
Three patterns of natural selection
Stabilizing Selection
- Individuals with intermediate phenotype favoured
- Extreme phenotype selected against
- Trait mean doesn’t change
Three patterns of natural selection
Disruptive Selection
- Both extreme phenotypes favoured; intermediate phenotype selected against
Modes of Selection
No selection
- When survival and reproduction are not random
Viability Selection
- Differences in survival
Fecundity Selection
- Differences in reproductive success
What defines male vs. female
- Gametes!
- Male produce abundant, smaller, energetically cheap, motile sperm
- Female produce few, larger gamete, energetically expensive, less motile eggs
Parental investment dif, men less than female
Parental care dif, cost of bearing (pregnancy) & raising offspring typically greater in female
Sexual Selection
- Purely success in having offspring
- Result of heritable difs in fertility &/or survival
- Darwin viewed as dif than nat sel, now we don’t
Moose antlers getting caught in trees, but fight other male for mates
Reproductive Success
- Females limited by resources
- Males limited by access to females (usually)
- Is = to fecundity + mating success
Sexual Monomorphism/Dimorphism
- Mono - Male and female look the same
- Di - Visual dif b/w male and female
Aspects of Sexual Selection
Intrasexual selection
- Fitness dif resulting from dif abilities of members of the same sex to compete (male-male competition, ape teeth/jaw)
Aspects of Sexual Selection
Intersexual selection
- Fitness dif resulting from preferential mating b/w specific males & females (mate choice, peacock with cooler colours competition)
Allopatric Speciation
- Geographically Isolated
- Physical barrier divides geographic range
- Gene flow ceases & separate pops evolve independently
- Over time, dif alleles become fixed, because of mutation + drift &/or selection
2 - vicariance event
Can also be a dispersal with half of pop, or a small pop leaves and small pop subject to drift forces
Confirm Allopatric Speciation
- Provided sufficient time has elapsed for divergence
- Barrier removed and pops go back in contact, stay distinct
- Interbreeding prevented via pre/postzygotic mechanism
Sympatric Speciation
- Pop in same geohraphic location
- Disruptive selection makes two distinct sub pops
- Sub pops diverge into 2 dif species
- Stages - Initial: Polymorphism that affects fitness. Then: Mating b/w 2 forms discourage (prezygotic) and or disadvantageous (postzygotic)
Polyploidization
- Can cause sudden speciation
- Meiosis fails & organism produces 2n gametes
Polyploidization
Autopolyploids
- Can only mate with another autopolyploid = reproductive isolation
- Caused if 2n gamete fertilized with another 2n gamete
Polyploidization
Allopolyploidization
- Similary to autopolyploid but involves first the mating b/w 2 closely-related species
Species Concepts
- Framework to address how to organize the discrete clusters of variation in nature
- Dif concepts place dif emphasis on dif factors
- 2 major categories
Species Concepts
Morphological
- Individuals look alike
- Most traditional concept
- Advantage: Practical, simple to use
- Disadvantage: No clear genetic or evo justification; choice of characters may be arbitrary
Species Concepts
Reproductive/Biological Species Concept (BSC)
- Ability to produce offspring
- Interbreeding natural pops
- Advantage: Clear criteria, clear evolutionary justification
- Disadvantage: Difficult to distinguish in the field - less of an issue with genomics
Species Concepts
Others: Phylogenetic/evolutionary
- Shared evolutionary history
- Common ancestry
- More useful when thinking asexual species
