Evolution Flashcards
Evolution
Complex species evolve from simpler pre-existing ones by a process of continuous and gradual change
Gene mutation
- random event resulting in a new allele
* can be harmful, neutral or beneficial
Microevolution
- populations gradually changing over many generations so that individuals with mutant alleles increase in frequency
- e.g. antibiotic resistance, heavy metal tolerance in grasses and pesticide resistance in rats
Macroevolution
Evolutionary changes at a higher level than species, resulting in the formation of a higher taxonomic group
Warfarin
- anticoagulant (Rat-poison)
- binds with and inhibits vitamin K epoxide reductase
- used in low concentrations as medicine for those at risk of stroke or heart attack
- high conc.; potentially lethal internal bleeding
- due to random mutation, after several generations, some rodent populations become resistant by evolving enzymes into which warfarin cannot bind so readily, or ones which break it down -> allele frequency increased
Vitamin k epoxide reductase
Catalyses the production of clotting factors
Morphs
Genetically distinct adult bodies experienced by many species (esp. insects) contained within the same interbreeding population
Hardy-Weinburg équations
- total frequency of alleles of a gene = 100%
- p + q = 1.0
- p = dominânt allele
- q = recessive allele
- p^2 + 2pq + q^2 = 1.0
- p = frequency of dominant homozygous genotype
- pq = frequency of heterozygous genotype
- q^2 = frequency of recessive homozygous genotype
Hardy-Weinberg equilibrium
- identifiés a mathematical relationship between the alleles and genes in populations
- ‘the frequency of dominant and recessive alleles in a population will remain constant from generation to generation’
Conditions of the Hardy-Weinberg equilibrium
- large population
- random mating
- no mutations
- no population immigration or emigration
- all genotypes are equally fertile; no natural selection
Why is large population a necessary condition for the Hardy-Weinberg equilibrium?
- excludes chance factors
- in small population there is a greater chance of allele frequency differing from generation to generation
- genetic drift
Genetic drift
- aka founder effect
- change in allele frequency due to chance
- May occur when a few individuals from a large population colonise isolated areas
- results in less genetic variation within the small population than the original population
- some alleles from the large, original population may become absent in the small populations; others may be disproportionality represented
If the conditions of the Hardy-Weinberg equilibrium are met…
… a change in allele frequency provides a means of measuring rate of evolutionary change
Genetic bottleneck
- caused by catastrophe
- population declines dramatically; only a few individuals act as a source of genes for future generations
- inbreeding is increased due to the reduced pool of possible mates
Boom-bust
- occurs in a closed system
* e.g. yeast
Closed system
- nutrients (e.g. O2) are not replenished
* not removing products (ethanol; toxic)
Natural selection
Occurs in open systems
Darwin’s observations
- within à population are organisms with varying characteristics; these variations are inherited (in part) by their offspring
- organisms produce more offspring than are required to replace their parents
- on average, population numbers remain relatively constant and no populations grows indefinitely
Darwin’s conclusion
- within a population many individuals do not survive, or fail to reproduce
- there is a ‘struggle for existence’
- individuals that are best adapted to their environment have a selective advantage
- they are more likely to survive and reproduce
Struggle for existence
creates selection pressures
Selection pressure examples
- limited resources (food/shelter) -> causes competition
- predation
- disease
- changes in environmental conditions
- lack of light/water/O2
What causes competition?
Over-reproduction
Carrying capacity
Plateau caused by competition
Selection pressure basics
- environmental change ([a]biotic) that results in genetic diversity
- environmental factors that keep populations from growing exponentially
High natality
Selective advantage