darwins observation
- Species in Africa should resemble species in Africa, but rather they resemble species in South America
- Influenced by Thomas Malthus: human species populating too much = limited resources
o Populations of species are constant b/c of death
o Struggle for existence = species w/ favourable traits survive
natural selection
- Those with favourable traits will overtake those with bad traits = evolution
- Increases differences in pops to produce pops suited for their environment
- Lyrell said the earth is old and Darwin used that to explain adaptation and biodiversity over time
population and fitness
- Population: local group of potential interbreeding individuals in the same species
o Defined by gene pool—sum total of alleles of all genes in the population
o Individual with favourable alleles has a higher chance to survive and interbreed
Its alleles will be present in next gen in next generation
o Fitness—rate of production for viable surviving offspring per time
hardy weinberg
- The ratio of dominant and recessive alleles is retained from each generation
- HW Equation: freq of alleles in a pop gene pool remain constant
o p2 + 2pq + q2 = 1
homozygous AA
homozygous aa
heterozygotes Aa
HW is true if
- This is true if: gene pool cannot be altered
1. No mutations
2. Isolation from other populations
3. Large pop size
4. Random mating
5. No natural selection—alters gene pool
microevolution
- Small scale gen-gen change in freq of a pop alleles
mutations
o Heritable changes in genotype
o Substitution in chromosome (small to large)
o Spontaneous and random but not w/o purpose
Not intended for good or bad
o Rate is low
genetic drift
o changes in gene pool due to chance
o Bigger pops are not affected
o Determines evolutionary track of small pops
gene flow
o Movement of alleles into or out of a pop (immigration or emigration)
o Introduce new alleles or change existing allele frequencies
o Overall effect is to decrease diff between pops
o Can diminish fast with distance
founder effect–genetic drift
Small pop separated by the larger one will not be a genetic rep of the larger one
* Some alleles are overrepresented or may be completely lost
Small pop increase in size it would have a diff genetic composition from the larger group
bottleneck effect–genetic drift
Pop is reduced in # by a natural event (earthquake)
Eliminate alleles entirely and some may be overrepresented
nonrandom mating
o Purposeful
o Inbreeding occurs in large population
Self-pollination does not change alleles but genotype frequencies
Increases freq of homozygotes
Decrease heterozygotes
o Does not change the frequencies in a pop but affects genotypic freq
responses to selection
- Epistasis—one gene affects the phenotypic expression of another gene at another at another locus
- Pleiotropy—one gene affects a # of phenotypic characteristics
adaptation
- State of being adjusted to the environment
- Variation in a trait that increases of the individual
coevolution
- Populations of 2 or more species interact closely exerts a strong selective force on the other, adjustment result in coevolution
biological species concept
group of interbreeding natural pops that are reproductively isolated
o Anything that can breed that gives something sterile, those 2 bred species are separate
o Isolation = species
o Hybridization: crossing of unlike parents
Hybrids are intermediates from their parents e.g habitats
phylogenetic species concept
statistically difference for traits to emerge
o Implies genetic isolation but does not require breeding test or complete genetic isolation to determine the species
morphological species concept
o Based on appearance
how does speciation occur
allopatric, sympatric, recombination speciation
allopatric speciation
o Geographic barrier arises—preventing gene flow from blending away any differences
Through selection or drift
o Mountains or valleys
o Short distances—accumulation of enough genetic divergence to make a reproductive isolation—infertility or inviability
o Islands have diversification of a group of organisms that have a common ancestor
Sudden diversification forming a new species with diff ecological roles and adaptation—adaptive radiation
sympatric speciation
o Polyploidy—cells that have 2+ sets of chromosomes
Due to nondisjunction—failure of homologs separating in meiosis
Due to failure to separate during cytokinesis in miosis
Autoploidy—doubling of chromosome # within an individual
Alloploidy—cross b/w two diff species creating an interspecific hybrid (mule)
* Sterile b/c chromosomes did not pair in meiosis
* Daughter has double chromosome as the parent
* Reproductively isolated from the parent
* Chromosome can pair if autoploidy occurs in sterile hybrid the cells can divide in mitosis and produce a new individual asexually
asexual reproduction
- Plants can do both (asexual and sexual)
- Asexually produce identical plants quickly and efficiently
- Clones can be useless if diseases fall upon them bc of their lack of genetic diversity i.e. potatoes
- Apomixis
o Formation of seeds w/ embryos that are produced without fertilization
Embryos are clones of mother
macroevolution
- Discontinuity in habitat and the accumulation of small changes in freq of alleles in gene pools
o Gradualism model
o Punctuated model–evolution occurs in spurts instead of following the slow, but steady path
recombination speciation
speciation
Two distinct species hybridize, the mixed genome of the hybrid a third species that is reproductively isolated from the parent species
