BIOLOGY 1B Lecture Notes - Lecture 3: Gregor Mendel, Allele Frequency, R.W.D. Molenbeek
11 Jun 2018
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Lecture 3: The Molecular Basis of Evolution
8/28
Gregor Mendel
• Researcher
• Learned importance of repetition of experiments and quantification of results
• Particulate inheritance
• Levels of organization
o Bases pair, gene, DNA, histones, nucleosomes, telomere, chromosome, nucleus, cell, individual,
population
• Gene flow:
o Two herds that don’t interact with each other- genes have distinct features
• Hardy Weinberg:
o Rules of Probability
▪ Rule of multiplication: probability that independent events A and B will occur
simultaneously
▪ Rule of addition: the probability that event A or B will occur is equal to probability A+
probability B
o Allele and genotype counts and frequencies
▪ Allele: variant form of a given gene, R, r
▪ Ex. 320 plants with red flowers, 160 pink, 20 white
• RR= red, Rr= pink, rr= white
• N= 500
• Proportion of RR= 320/500= 0.64= 64%
• Proportion of Rr= 0.32= 32%
• Proportion of rr= 20/500= 0.04= 4%
• # R alleles= 320(2) + 160(1) + 20(0) = 800
• # r alleles= 200
• Allelic frequencies :
o F(R) = 800/1000= 0.8
o F (r) = 200/1000= 0.2
o F (R)= p ; F(r)= q
o The Hardy Weinberg Principle”
▪ P + 2pq + q2= 1
▪ Population assumptions:
• No mutations
• Large
• Isolated (no gene flow)
• Random mating
• No natural selection
• Under these conditions, allele frequencies in the gene pool will NOT change
• Modern Synthesis/ Neo-Darwinism
o Microevolutionary forces:
▪ Mutation: replacement of single nucleotide and incorrect amino acid
▪ Genetic Drift: occurs because populations are not infinitely large
• Produces random changes in allele frequencies
• Involves roles of chance
• May lead to loss of genetic variation in a population
• May cause particular alleles to become very common or even fixed
• More likely in smaller populations
• The founder effect: small number of individuals find population; reduction of
genetic diversity
o Ex. Amish people have a high frequency of the Ellis-van Creveld
syndrome (Extra fingers and toes) because of the lack of gene flow in
and out of the population
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