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Lecture 2

BIOL 1020U Lecture 2: CH 21_Evolution WF Notes

Course Code
BIOL 1020U
Annette Tavares, Mary O.

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Evolution Lecture
Chapter 21 (pp. 21.1 - 21.8)
Adaptation, Unity and Diversity
Three key observations about life:
1. Organisms suited to their environments- adaptations
2. Shared characteristics (unity)
3. Rich diversity
Grasshopper: camouflage
oCamouflage is often a dramatic example of adaptation
Headstander beetle: ability to obtain water -uses water droplets in fog
Genetic Variation
Since Darwin, we have appreciated that species do not conform to a type and
instead consist of a range of variants.
What does natural selection depend on? – it depends on the differential success,
in terms of surviving and reproducing, of variants
Humans – high degree of phenotypic variation, but we actually rank low in terms
of overall genetic variation compared to other species
Comparison of genetic variation:
Phenotypic variation Overall genetic variation
Humans High degree Low degree
Is about 10 times more
variable than we are in
terms of the number of
DNA bases that differ from
one individual to the next
Adelie penguins
Low degree of phenotypic
variation but are actually 2-
3 times more genetically
variable than we are!
Population genetics is the study of patterns of genetic variation in natural populations
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Important terminology:
Species – a group of individuals that can exchange genetic material
through interbreeding, or share alleles through reproduction
Gene pool – all the alleles present in all individuals in a species
Populations – an interbreeding group of organisms of the same species
living in the same geographical area
What can cause genetic variation?
Mutation - generates new variation
– Somatic
– Germ-line
– Deleterious
– Neutral
Advantageous adaptations
Shuffles mutations to create new
combinations of mutations –both of
which result in new alleles being formed
Measuring Genetic Variation
Allele Frequencies
To measure genetic variation in a population you must know: the rates of
occurrence of the alleles In the population
Frequency of an allele is simply the number of that particular allele present in a
population divided by the total number of alleles
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