BIO372 : Evolution : Natural Selection & Adaptation : Lesson

I. Evolution of Darwinism

1. Synthetic theory of evolution: The Modern Synthesis
   • Variation occurs among individuals in a population
   • Variation results from genetic mutation which occurs by chance
   • Better adapted individuals leave more offspring
   • The environment selects

2. Hypotheses
   • Molecular determinism: evolution proceeds independently of chance and natural selection
   • Neutral theory: initial appearance of genetic variations and their subsequent establishment in the population both occur by chance
   • Punctuated equilibrium: evolution proceeds at an irregular pace

3. Molecular evolution
   • Relation of genes to development
   • Genetic variation is complex
   • Amount of genetic information increases in evolution
   • Polyploidy: produces multiple sets of genes

New Genes Tandem multiplication Repetition of a nucleotide sequence in adjacent sites along a chromosome Occurs during crossing-over when chromosomes pair out of alignment Collagen in chickens Total length of 38,000 np More than 50 exons separted by introns Exons consist of a repeated sequence nine nucleotides long

5. Immunoglobulins (antibodies)
   • Consist of 2 large (heavy) and 2 smaller (light) polypeptide chains
   • Variable region of heavy chain resulted from 12 tandem repetitions of a 48 np sequence
   • Constant region of heavy chain consists of four components each coded for by a separtate exon

6. Gene Duplication
   • Occurs during crossing-over
   • Duplicate gene develops its own character
     • Globin genes: from plants to vertebrate muscle and blood
     • Pseudogenes: non-functional duplicate

7. Variaton
   • Rate of evolution is proportional to the amount of genetic variation within the population
   • Electrophoresis
     • Degree of heterozygosity ranges from 5-20%
     • More variation is present than electrical charge reveals
     • Redundancy of DNA suggests that organisms may be heterozygous at almost all gene loci

8. Neutral Theory
   • Some genetic variation confers an adaptive advantage and some does not
   • Redundancy in the genetic code produces mutations
   • Sickle-cell hemoglobin
     • One amino acid is the difference between normal and sickle-cell hemoglobin
     • Homozygous condition is lethal
     • Heterozygous condition is resistant to malaria

9. Molecular Clock
   • Rate of DNA change is fairly constant over long periods and can be used to infer evolutionary distance

10. Punctuated Equilibrium
    • Periods of rapid change alternate with periods of little change
    • Time Scales: fossils in the geological record reflect evolution in a "few" generations

11. Mosaic evolution
    • Different parts of an organism do not change at a uniform rate: some characteristics may remain constant for long periods while others change rapidly
    • Archeopteryx
    • Australopithecines
    • Hominids

12. Morphology and Speciation
    • Changes in appearance (morphology) happen in response to new environmental challenges
    • New species arise when populations become spatially separated
    • Hemp nettle hybrids: genes for morphology and reproductive compatibility were not limited
    • Drospohila: morphologically similar species coexist by exploiting the environment in slightly different way
    • Tanweed (Holocarpha): similar morphology but reproductively incompatible
    • Buckbrush (Ceanothus): morphologically different but reproductively compatible

II. Crop Circles Every hypothesis has its faithful, no matter the evidence

When you have completed this lesson, go on to Review Questions