Bio. 230 --- Evolution III

Some History of Evolutionary Thought Empedocles (Greek, ~490 to 430 B.C.) 1st to propose a clear concept of biological evolution Abiogenesis Plants arose 1st; their buds gave rise to animals Gradual process

Some History of Evolutionary Thought Aristotle (Greek, 384-348 B.C.), student of Plato (~427-347 B.C.) Similar ideas Abiogenesis Acquired characteristics Species could hybridize

Some History of Evolutionary Thought Lamarck (French, 1744-1829) 1st in more modern times to put forth a comprehensive & logical evolutionary theory Acquired characteristics Pangenesis / pangenes Newer forms were more complex (and “perfect”) than their ancestors

Some History of Evolutionary Thought Charles Darwin (English, 1809-1882) Started out as a special creationist READ handout: “A comparison of views on variation and heredity” 1831-1836 --- voyage on the Beagle Then worked for more than 20 years 1838 – He read AN ESSAY ON THE PRINCIPLE OF POPULATION by Thomas Malthus Natural Selection

Some History of Evolutionary Thought Charles Darwin (English, 1809-1882) 1844 -- Put together a brief essay (unpublished) Early 1858 – Essay from Alfred Russel Wallace Later 1858 – Published Wallace’s essay and excerpts from his own 1844 essay in the Journal of the Linnaean Society 1859 – published THE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION

Darwin’s Main Points Overproduction of offspring Variation within a species and at least some of it is hereditary Limits on resources; engenders a struggle for existence Generally the fittest survive (= Natural Selection) Eliminating of unfavorable traits and accumulation of more favorable traits gives rise to new forms of life

NeoDarwinism or The Modern Synthetic Theory Darwin did not have all the answers 1937 – Theodosius Dobzhansky (Genetics and the Origin of Species) began the MST 1950s to 1970s additional seminal work C. Leo Babcock (plant evolution), Edgar Anderson (Introgressive Hybridization), Earnst Mayr (animal evolution), G. L. Stebbins (plant evolution), J. Watson & F. Crick (DNA structure), M. Nirenberg & J. H. Matthaei (genetic code)

Evolutionary Potpourri Evolution occurs in POPULATIONS* Populations can have a change in gene / allele frequency All populations are phenotypically polymorphic New gene / allele combinations can come about from CROSSINGOVER and RECOMBINATION during sexual reproduction New alleles / genes come about by some type of MUTATION Microevolution* vs. Macroevolution* Are the processes that drive each different? Gradualism vs. Punctuated Equilibrium*

The Gene Pool (I) DEFINITION* -- ALL of the genes AND alleles in a population taking into account their frequency It is the total supply of genetic units available to form the next generation Not possible to study the whole gene pool Will look at a “mini” gene pool (for the gene “A”) Only two alleles: A and a 3 possible genotypes (AA, Aa, aa) We start a population with a certain frequency of A and a

The Gene Pool (II) What will happen to the allele (and genotype) frequencies over the generations?????????? Solved independently in early 20th century by: George Hardy & Wilhelm Weinberg Known by various aliases: Hardy-Weinberg Equilibrium Hardy-Weinberg Theorem Hardy-Weinberg Law

Hardy-Weinberg Equilibrium DEFINITION* -- Given certain conditions the allele frequencies remain constant from generation to generation AND after one generation of random mating even the genotype frequencies will remain constant and can be predicted from the equation (p + q)2 = p2 + 2pq + q2 p = the frequency (f) of A q = the frequency (f) of a p2 = f AA, 2pq = f Aa, q2 = f aa

Hardy-Weinberg Conditions (I) Infinitely large Population Eliminates chance fluctuations (genetic drift) Random Mating Means no inbreeding; no positive (+) or negative (-) assortative mating No net mutation Eliminates mutation pressure No net population movement Eliminates net gene flow

Hardy-Weinberg Conditions (II) No natural selection Means no type is better than another; all types must survive at proportional rates ----------------------------------------------------------------- “Survival of the Fittest” does not mean that organisms fight or that organism have to die Death (real) vs. Genetic Death Natural Selection works on PHENOTYPE

Genetic Drift A change in the allele frequencies in a gene pool due to random (chance) events More likely to happen in small populations OR when a small sample is taken from a large population Due to random sampling in a less than infinite population

Genetic Drift

Genetic Drift / Bottlenecking / Founder Effect

Many concepts; none are ‘perfect’ Morphospecies (= typological sp.) Some Species Concepts Many concepts; none are ‘perfect’ Morphospecies (= typological sp.) Biological species (= reproductive sp.) (E. Mayr) Phenetic species Ecospecies Phylogenetic species

Phyletic Speciation (Anagenesis) Number of extant species does not increase

Divergent Speciation (Dichotomous speciation or Cladogenesis) Number of extant species increases

Isolating Mechanisms See handout

Autopolyploidy (Fig. 24.10) ???????????

Allopolyploidy (Fig. 24.11) ???????????

Allopolyploidy (MOST likely) (2 pathways --- many examples) (Primula kewensis and Tragopogon mirus)