EVOLUTION : Introduction to Darwinian Evolution

Posted on February 23, 2009


>Learning objectives:
Discuss the historical development of the theory of evolution
Define evolution and explain the four premises of evolution by natural selection as proposed by Charles Darwin
Compare the synthetic theory of evolution with Darwin’s original theory of evolution

Summarize the evidence for evolution obtained from:
the fossil record,
comparative anatomy,
distribution of plants and animal (biogeography)
developmental biology,
molecular biology.
A. Introduction
biological diversity
microevolution (short term adaptation)
macroevolution (speciation)
B. Ideas about evolution originated before Darwin
Aristotle (384 – 322 B.C.) : natural affinities among organisms
Leonardo da Vinci (1452 – 1519): fossil, remain of extinct organisms
Jean Baptiste de Lamarck (1744 – 1829): Philosophie Zoologique
C. Darwin’s voyage was the basis for his theory of evolution
The H.M.S. Beagle voyage (1831)
Studying animals, plants` fossils and geological formations
Principles of Geology (Charles Lyell, 1830)
Artificial selection: colewort – cabbage, broccoli, Brussel’s sprout, cauliflower, collard greens, kale and kohlrabi.
Thomas Malthus (1798): population grow geometrically, but food supply grow arithmetically

D. Darwin proposed that evolution occurs by natural selection
The origin of species by means of Natural selection (1859)
Darwin’s mechanism of evolution by natural selection:
limits on population growth
differential of reproductive success
Natural Selection
Inherited variations favorable to survival tend to be preserved
BUT unfavorable variations tend to be eliminated
Adaptation: an evolutionary modification that improve survival & reproductive success in a given environment
Accumulation of modification might result new species

Natural selection
Alfred Russell Wallace (1823 –1913) had the same idea
Joint presentation of Darwin-Wallace at Linnean Society (London, 1858)
Contribution to the Natural Selection (Wallace, 1870)
E. The synthetic theory of evolution combines Darwin’s theory and genetics
At the population level: evolution ; the change of gene frequency
Evolution factors:
natural selection
gene flow (immigration or emmigrantion)
genetict drift
F. Many types of scientific evidences support evolution
The fossil record provides strong evidence of evolution
Comparative anatomy of related species demontrates similarities in their structure
The distribution of plants and animals supports evolution
Developmental biology is increasingly being used to explain evolution
Molecular comparisons among arganisms provides evidence for evolution
G. Bacteria and other organisms that cause infectious disese are evolving resistance to drug

Multiresistant-Drug TB : Mycobacterium tuberculosis
Antibiotic resistance : selection of resistant bacteria in the bacterial population
A. Learning objectives:
Define population, genetic equilibrium, and microevolution
Distinguish among genotype, phenotype and allele frequencies
Use the Hardy-Weinberg principle to solve problems involving populations
B. Calculation of :
genotype frequency
phenotype frequency
allele frequency:
The frequency of Homozygous dominant
The frequency of Heterozygous
The frequency of Homozygous recessive
C. Genetic equilibrium : the Hardy-Weinberg principle
p : the frequency of the dominant (A) allele in the population
q : the frequency of the recessive (a) allele in the population
p + q = 1 ( p = 1 – q; q – 1 = p)
(p + q)2 = (1)2
p2 + 2pq + q2 = 1
p2 : frequency of AA
2pq: frequency of Aa
q2: frequency of aa
1 : all the individuals in a population
D. Genetic equilibrium occurs if certain conditions are met:

Random mating
No net mutation
Large population size
No migration
No natural selection
Genotype Frequency: a population of 1000 individuals
Phenotype frequency
Allele frequency
Individuals: diploid – has 2 alleles: thus 1000 individuals = 2000 alleles

490 AA individulals x 2 = 980 A
420 Aa individuals x 2 = 420 A + 420 a
90 aa individulas x 2 = 180 a
Total 1400 A + 600 a
Allele Frequency
Calculation of allele frequency & genotype frequency from the phenotype frequency
Always start Hardy-Weinberg calculation by determining the frequency of the homozygous recessive genotype (aa)
The frequency of aa genotype = 90/1000, thus the frequency of (q2) = 0.09
The frequency of a recessive allele (q) =√0.09
(q) = 0.3
Allele Frequency
p = 1 – q
p = 1 – 0.3
p = 0.7 (the frequency of dominant allele)
p2 = 0.7 x 0.7
p2 = 0.49 (the frequency of homozygous dominant individuals)
2pq =2(0.7 x 0.3)
= 0.42 (the frequency of heterozygous individuals)
Allele Frequency
Thus, q2 = 0.09 x 1000 = 90 individuals
p2 = 0.49 x 1000 = 490 individuals
2pq = 0.42 x 1000 = 420 individuals
This follow: p2 + 2pq + q2 = 1
(0.49) (0.42) (0.09)

Conclusion: the population is at genetic equilibrium !

Posted in: BIOLOGI