BIOL 2020U Lecture Notes - Allele Frequency, Speciation, Meiosis
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Variation is the presence of any differences (genotypic and phenotypic), between
individuals in a population, or between parents and offspring.
Genotypic variation can be due to:
o Random assortment during Meiosis,
o Crossing over during Meiosis,
o Random fertilisation of gametes.
Phenotypic variation can be due to:
o Genetic Factors,
o Environmental Factors,
o Combination of both.
Variation provides organisms with a means of producing new phenotypes.
Variations to the structure or behaviour of an organism may confer a selective advantage
to survive and reproduce
Evolution is the sum of changes of heritable characteristics in population.
It is the development of life in geological time
Natural selection is the process where organisms that are better adapted to their
environment survive and breed.
Those that fail to adapt will not survive.
The environment therefore exerts a selection pressure on the population.
Allele frequency is the commonness of the occurrence of any particular allele in a
Evolution changes allele frequency in population because:
o Organisms with a selective advantage:
more likely to survive → reproduce → pass on genes to next
This will increase the frequency of the allele that corresponds to the
o Organisms with a selective dis-advantage:
less likely to survive → die → fail to pass on genes to next generation.
o This will decrease the frequency of alleles possessed by these individuals.
A population is a group of individuals of a species, living close together, and able to
Populations reproducing in isolation can result in the formation of new species
This is known as Speciation.