Microevolution
I.INTRODUCTION
A.Evolution
1.Generation to generation in allelic or genotypic frequency
a)Change in a population genetic structure
(1)Only one loci needs to be changing for population evolution
(2)No such thing as individual evolution
II.GENETIC DRIFT
A.Too small a population size
1.Sampling error
a)1000 coin tosses (500:500)
b)5 coin tosses (2:3 = 400:600)
2.Common in population under 100 individuals
B.Example
1.Parent generation
a)AA - Aa - aa
b)A = 50%; a = 50%
c)Perhaps the homozygous dominant individuals do not mate, therefore, the heterozygote and homozygous recessive only leave offspring
2.F1 generation
a)Aa - Aa - aa - aa
b)A = 20%; a = 80%
C.Bottle neck effect
1.Unselective killing
a)Earthquakes, fires, flooding, hunting
2.North American elephant seal
a)Hunted to 20
b)Numbers up to 30,000 since protected
c)Genes fixed at 20 loci examined
3.South American elephant seal
a)Not hunted
b)Multiple alleles at all loci examined
D.Founder's effect
1.A few individuals colonize a new habitat
a)Ponds, islands, etc.
b)Even just one, if pregnant or with seed
2.Tristanda Cuhna (a British colony)
a)Founded in 1814 by 15 persons
(1)One carrier of the recessive allele for retinistis pigmentosis
b)Population at 240 in 1960
(1)4 showed trait and 9 were carriers
III.GENE FLOW
A.Perhaps pollen from white flower pollinates a population of red flowers
1.Might result in some pink flowers
2.Preference of pollinators for flower color will effect the fate of the white allele
IV.MUTATIONS
A.Original source of allelic variation
B.Types
1.Neutral
a)Fingerprints
2.Advantageous
a)House fly and DDT
b)Antibiotic resistance in bacteria
c)Sickle cell anemia
3.Disadvantageous
a)Phenylketonuria
C.Not much by itself without selection
V.NON-RANDOM MATING
A.Types
1.Interbreeding / self fertilization
2.Assortive mating
a)select partners like themselves
B.Effect
1.Increases the number of homozygotes and decreases number of heterozygotes
a)With random mating you might expect 1:2:1 ratio of genotypes, but with non-random mating you might get a 1:1:1 ratio
b)AA x AA = AA + AA; aa x aa = aa + aa; Aa x Aa = AA + Aa + Aa + aa
2.Allelic frequency does not change, but genotypic frequency is altered
a)Recessive phenotype is increased
(1)Often defective, hence taboos against close marriages
VI.SELECTED CONTRIBUTORS TO THE THEORY OF EVOLUTION
A.Carolus Linnaeus
1."Father of Taxonomy"
a)Noticed organisms had similarities and differences and grouped them together
(1)Came up with the kingdom, phylum, class, order, family, genus, species system
(2)Did not try to explain similarities and differences
(a)Species were assumed to be non-changing
B.Charles Lyell
1.Gradualism
a)Slow, but continuous change
(1)Canyon's cut by rivers
(2)Sedimentary rock formation
b)Age of Earth was much older than originally thought
C.Jean Baptist Lamarck
1.Proposed that acquired traits may be a mechanism for evolution
a)Often called the "Doctrine of Use and Disuse"
b)Though later the mechanism was shown to be incorrect, it opened the pathway for other proposed mechanisms for evolution
D.Charles Darwin and Alfred Wallace
1.Proposed natural selection for mechanism of evolution
a)Descent explains the unity of life
b)Modification explains the diversity of life
c)Direction of change is determined by natural selection
E.Gregory Mendel
1.Gives mechanism for evolution
a)Genes from parents determine phenotype and genotype
b)Genes could be mutated
VII.NATURAL SELECTION & ADAPTATION
A.Observation 1
1.All species have greater ability to reproduce than there are resources to support
B.Inference 1
1.Production of more offspring than the environment can support leads to a struggle for resources, with only a fraction of the offspring surviving each generation
C.Observation 2
1.No two individuals are alike
2.There is much variation with in a population
D.Observation 3
1.Much of this variation is heritable
E.Inference 2
1.Survival is not random, but depends on the heredity of the surviving individual. Those individuals whose inherited characteristics fit them best to their environment are more likely to leave more offspring than less fit individuals.
F.Inference 3
1.This unequal ability of individuals to survive and reproduce can lead to gradual changes in a population, with favorable characteristics accumulating over the generations