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
High mortality
Selective disadvantage
The difference in natality and mortality results in
Natural selection
Fitness
- the ability of an organism to pass on its alleles to subsequent generations, composed of individuals of the same species
- the fittest organism is the one that produces the largest number of offspring that survive to reproduce themselves
Natural selection means that…
… the genetic characteristics of a population gradually change from generation to generation…
… this affects a gene pool by increasing frequency of advantageous alleles, and decreasing frequency of disadvantageous alleles
Gene pool
The sum of all alleles within a population (that is interbreeding)
The process of natural selection
1) a random and rare mutation occurs at the gene coding for the characteristic
2) this mutation causes genetic variation in a population due to the production of a different advantageous allele
3) the characteristic is advantageous because it provides a selective advantage
4) the organisms with this mutation are more likely to survive and reproduce, pass on this allele, and thus the allele is inherited by the offspring
5) the allele becomes more popular throughout the population- increases in gene frequency in the gene pool
6) phenotype is expressed in larger proportion through the generations
7) further increase in genetic variation could result in speciation
Types of selection
1) directional
2) stabilising
3) disruptive
Directional and disruptive selection are…
- less common
- caused by environmental change
- standard deviation shifts
Directional selection
- individuals with a more extreme characteristic are more likely to survive and reproduce
- e.g. antibiotic resistance
Describe antibiotic resistance
- parent generation exposed to an antibiotic
- only those with the alléle for resistance will survive and reproduce
- resistance allele increases in gene frequency in offspring populations
- mean amount of antibiotic resistance increases
Standard deviation curve shifts…
Towards the phenotype of the next generation
Stabilising selection
- extrême characteristics make an organism less likely to survive and reproduce
- causes a reduction in variation
- mean of SD remains the same
- e.g. birth weight
Describe how birth weight is a stabilising selection
- light -> high SA:Vol
* heavy -> complications
Disruptive selection
- selects against intermediate phenotypes and favours those at both extremes
- May have contributed to the evolution of Darwin’s finches
- leads to binomial distribution
- if the two groups become unable to breed, each population may give rise to a new species -> speciation
Describe disruptive selection in Darwin’s finches
- finches with short, strong beaks have exclusive use of nut food source due to lack of competition
- long, slender beaks have exclusive use of insects
- finches with average, unspecialised beaks were more likely to have been in competition w/ other species of bird; reproduced less successfully
Bimodal distribution
- SD has two peaks (modes)
* two overlapping groups of phenotypes
Speciation
One species splitting into two, resulting in the formation of a new species (or 2)
Causes of speciation
A mutation that causes genetic variation so extreme that the organisms can no longer produce fertile offspring
What can mutations result in?
- structural changes
- behavioural changes
- physiological changes
Structural changes
No longer look alike; do not want to mate
Behavioural changes
Mating techniques change
Physiological changes
Changes to the reproductive systems
Adaptations
Any variation that causes a selective advantage (increases chances of survival and reproduction)
Adaptations can be..
1) behavioural
2) physiological (biochemical)
3) structural (anatomical)
Describe behavioural adaptations
- happens more quickly
- the more intelligent the animal is, the faster it can learn to make behavioural changes for survival
- e.g. courtship dances/songs to attract mates
- e.g. moving in groups for protection against predation
Describe physiological adaptations
- ensures correct biochemical and physiological functioning necessary for survival
- e.g. hibernation
- e.g. long loops of Henle (water conservation)
- e.g. ability of anaerobically depending on O2 availability
Describe hibernation as a physiological adaptation
- lower metabolism in winter to conserve energy
* avoids the need to look for food in the months when food is scarce
Describe structural adaptations
- beak structure
- fur thickness and colour
- blubber -> insulation and energy store
- xérophytes
- streamlined shape -> faster movement to flee predators and catch prey
- flagella
Describe xerophytes
- plants adapted to living in hot and dry and climates
- shallow, spreading, long, penetrating roots for maximum water absorption
- fleshy stems store water
Peppered moth
- Biston betularia
- morph is determined genetically; the allele for melanism has a single gene location
- typica -> pale, speckled
- insularia -> intermediated, partly melanic
- carbonaria -> melanic
Describe industrial melanism
- increase in frequency of melanic moths due to air pollution
- caused by selective predation by birds
- the birds produced the main selection pressure by feeding differentially on months according to their background (presence of lichens)
Reduction of air pollution has caused…
An increase in typica morph
Sickle-cell anaemia
- caused by a single gene with two alleles: Hb^A and Hb^S
- Hb^AHb^A = normal blood
- Hb^AHb^S = sickle-cell trait; many struggle with high O2 demands (exercise, altitude)
- Hb^SHb^S = abnormal blood; sickle cell anaemia can be fatal -> the allele has not been eliminated
Malaria
- Plasmodium
- single-celled protoctist parasite
- introduces into blood via mosquito bite
Hb^AHb^S
Much less likely to suffer serious malaria
Hb^AHb^A
Much more likely to suffer serious malaria
Selection pressures on sickle-cell anaemia in malaria infested areas
- strong selection pressure for Hb^SHb^S
- strong selection pressure for Hb^AHb^S
- Hb^AHb^A has a selective disadvantage
- heterozygous advantage
- allele frequency depends on amount of malaria:
• no malaria, no sickle-cell anaemia (excluding migration)
The net result for sickle cell anaemia of the opposing selection pressures means that…
… the sickle-cell anaemia allele is retained in places where malaria is a significant environmental factor
