• process in which individuals best suited in the environment survive and reproduce naturally to produce their phenotype offsprings.
  • selection pressure is exerted by environmental factors eg presence of light and nutrients may affect the survival of plant organism in a given area.
  • it results in competition for light and nutrients.
  • the best adapted organism only survive to reproduce whilst other organisms die.

 

The role of natural selection in evolution.

  • individuals in population have great reproductive potential;
  • in population remain roughly constant ;
  • many fail to survive / die ;
  • do not reproduce ;
  • due to environmental factors / named factor ;
  • variation in members of population ;
  • those best adapted survive ;
  • reproduce / pass on alleles ; R genes
  • genetic variation leads to change in phenotype ;
  • ref: changes in gene pool ;
  • over time produces evolutionary change ;
  • new species arise from existing ones

 

Why variation is important in natural selection.

  • ref. continuous / discontinuous variation ;
  • genetic / inherited variation ;
  • variation in phenotype / characteristics ;
  • (can be due to) interaction of genotype and environment ;
  • e.g. of characteristic that influences survival ;
  • ref. intraspecific competition / struggle for existence ;
  • those with favourable characteristics survive / AW ;
  • pass on favourable characteristics to offspring ;
  • those with disadvantageous characteristics die ;

How natural selection may bring about evolution.

  • individuals in population have great reproductive potential ;
  • numbers in population remain roughly constant ;
  • variation in members of population ;
  • environmental factors / named factor (biotic or abiotic) ;
  • (cause) many, fail to survive / die / do not reproduce ;
  • those best adapted survive / survival of the fittest ;
  • (reproduce to) pass on alleles ; R genes
  • genetic variation leads to change in phenotype ;
  • ref: changes in, gene pool / allele frequency ;
  • over time produces evolutionary change ;
  • new species arise from existing ones / speciation ;
  • directional / stabilizing, selection ;

Diffenceres between natural and artificial selection

Artificial selection natural selection
Selection pressure applied is by humans Environmental selection pressure
Genetic diversity is lowered Genetic diversity remains high
Inbreeding is common Outbreeding is common
inbreeding depression less inbreeding depression
Increased homozygosity Decreased homozygosity
Usually faster Usually slower
Not for survival/evolution Promotes survival/evolution
No isolation mechanisms operating Isolation mechanisms do operate

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