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Lecture 16

Lecture 16 Notes


Department
Biology
Course Code
BIO120H1
Professor
Doug Thomson
Lecture
16

Page:
of 4
BIO120
LECTURE 16: MEASURING GENETIC DIVERSITY
Fisher & Haldane: quantitative aspects of evolutionary change; population genetics into evolution
Wright: mendelian law, natural selection, and continuous variation – mathematical
Synthesis of ecology (Darwinian natural selection and genetics)
Theory of impericism.
Not all genes are variable
What forces influence diversity?
Mutation
Recombination
Random genetic drift ( small population size effects)
oCan lead to reduction in diversity
Natural selection
oPurifying ( negative)reduce fitness removed by selection
oPositive selection (adaptation)mutatuion arises and is favoured.
oBalancing selection – heterozygotes are favoured over homozygotes
Fisher felt that all important evolution occurred in large population by natural selection; genetic drift=
unimportatn
Wright – genetic drift played important role in evolution
^CONTROVERSY IN EVOLUTIONARY BELIEFS
Importance of mechanism:
Mutation-selection balance
Mutation and strength of selection
Natural selection taking mutatuions out
Differet selective forces
www.notesolution.com
Frequency of geno and phenotypes in population
1:1 sex ratio in animals; the minority sex will have an advantage in mating;m
Ratio maximizes fitness
Variation selectively neutral
John Kelly: artificial selection
Monkey flower
oFlower sizelow and high
oOriginal plants collected from natural population
oAble to get big and small flowers in only 5 generations
oControlrandom mating
oVariation within a single population and species
Cannot measure polymorphism and heterozygosity
Need measurements of genes that control traits that everybody has
Need to make a model that can make predictions
Morgan and Mullerlab based scientists (CLASSICAL SCHOOL)
Most mutations are bad
Dozhansky – field scientistsaw genetic diversity (BALANCE SCHOOL)
Ford – how much diversity should be in natural populations? (BALANCE SCHOOL)
WHO WAS RIGHT?
Occasionally a new allele would arise and zygotes would spread
CLASSICAL SCHOOL
Wild type allele is replaced by another wild type
Rise in frequency
Did not predict there would be alot of polymorphism
www.notesolution.com
There is one genotype that is the fittest
BALANCE SCHOOL
Predicted variablility is the normal condition
Field work
High diversity and polymorphism
No best genotype
www.notesolution.com