Selection And Speciation- Paper 2 Flashcards
What are the 3 causes of variations?
- Mutations- causes combination of new alleles which may cause a new phenotype
- Meiosis- caused by independent segregation and crossing over
- Random fertilisation and fusion of Gametes during sexual reproduction
What are features of variation which is caused by genet factors?
It is discontinuous, which produces categoric data and is usually caused by a single gene.
What could a mutation be?
A selective advantage
Neutral as the code is degenerate
A selective disadvantage, inhibits gene and selects against advantageous alleles
What are environmental influences
Abiotic and biotic factors, the environment influences the organism’s phenotype and the way the genes are expressed
Define natural selection
A process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population
What determines the spread of an allele within the gene pool
Selection pressures, they are either abiotic or biotic
Stabilising selection
Occurs in populations where the environment is stable
Selection pressures at both ends of distribution
Favours the average
Tends to eliminate extremes
Reduces variability, the size of the range within population
Reduces opportunity for evolutionary change
Directional selection
Mean in population represents optimum phenotype for existing conditions
Environmental change may produce new selection pressures that favour an extreme phenotype
Changed conditions, favour allele combination necessary for survival
Some organisms will possess the new optimum phenotype
Over time selection means this allele combination will predominate and the mean phenotype will shift
Disruptive selection
Environment has selective pressures that favour two extreme phenotypes
When conditions change the optimum phenotypes necessary for survival will also change
Some organisms will possess the new extreme optimum phenotypes
Over time selection of these two extremes will dominate and the mean will shift in both directions
Species definition and facts
The evolution of a new species from an existing species
Species belong in the same gene pool
Two populations must undergo a period of reproductive isolation to become genetically distinct through an accumulation of mutations and different selection pressures
Genetic drift description
Random increase or decrease in allelic frequency, important in small populations where the loss will result in significant change to the frequency. May occur from natural disasters such as volcanic eruption
gene flow description
Change in allelic frequency due to the migration of fertile individuals, such as migration
Allopatric speciation
Geographical isolation- a physical barrier divides a population. Each population may be subjected to different selective pressures,mutations accumulate, change in genotype and phenotype , reproductively isolated, each population has become separate species with its own gene pool
Sympatric selection
Organisms in same area become reproductively separated either from choice of food or choice of season to mate in or become active after hibernation.
Other isolating mechanisms: temporal
Organisms breed at different times of the year
Other isolating mechanisms: Ecological
Different habitats within same area
Other isolating mechanisms: Behavioural
Different behaviour patterns eg courtship behaviour
Other isolating mechanisms: mechanical
Anatomical differences making it impossible for games to come together
Other isolating mechanisms: gametic
Incompatibility between gametes prevent hybrid from forming
Other isolating mechanisms: hybrid
Organisms interbreed but offspring are infertile
Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. this led to the formation of a number of different species of pupfish. Explain how these different species evolved
Geographical isolation
Separate gene pools
Variation due to mutation
Different environmental pressures
Selection for advantageous allele
Differential reproductive success
Leads to change in allele frequency
Occurs over a long period of time
It has been suggested that a new species of grass may evolve on soil that has been polluted with copper. explain how this new species may evolve
Variation caused by mutation
Some plants have allele to survive
Differential reproductive success
Increase in frequency of advantageous allele
Not interbreeding with other populations
using this information, suggest how these two species of palm tree arose by sympatric speciation
Occurs in same habitat
Mutations cause different flowering times
Reproductive isolation, gene pools remain separate
Change in allele frequency
Disruptive natural selection
Eventually different species cannot interbreed to produce fertile offspring
Guppies with large brains are better at identifying predators. The scientist found that only female guppies with large brains were attracted to male guppies bright in colour
females mate with males bright in colour, offspring will be bright in colour so will attract larger brained females , more reproduction of fish with larger brained females, population are better at identifying predators
Explain how different subspecies of giraffe may have evolved from a common ancestor
No interbreeding, gene pools are separate
Mutation linked to different markings
Selection linked to markings
Adapted organisms breed
Change in allele frequency
Describe how you could use the mark-release-recapture method
Capture, mark and release
Method of marking does not harm organism
Leave sufficient time for lizards to randomly distribute before collecting a second sample
Population= number in first sample x number in second sample/ number recaptured
