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Chapter 24

BIOLOGY 1M03 Chapter 24: Chapter 24

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Ben Evans

Chapter 24: Evolution by Natural Selection Key Concepts Evidence of Evolution: change through time (fossils), extinction, vestigial traits, inter- relatedness Evidence of Natural Selection: industrial melanism, antibiotic resistance, beak size in Galapagos finches Natural Selection affects individuals, but evolution occurs in populations over time (epigenetics) • Darwin and Wallace proposed that change in species over time is based on natural selection acting on heritable variation among individuals • Darwin described evolution as decent with modification, meaning that change over time produced modern species form ancestral species Species: o change throughout time o are related by common ancestry ex. Lobed finned fish vs. early amphibian Fossils • Trilobite fossil from BC, Canada; 505 million yrs old • Hominoid footprints from Tanzinia 3.6 million yrs old Extinction • Many fossils provide evidence for extinct species, those that are no longer living Prehistoric Turds and ancient DNA • Groundhog very large feces Transitional Forms • As the fossil record has been come more complete, many transitional forms have been discovered with traits that are either intermediate between earlier and later species Ex. Limb development and loss, feathers and flight, upright posture and brain size in humans, jaws in vertebrates Vestigial Traits • Loss or gain of a trait Ex. Loss of think body hair in humans Ex. Loss of long tails in apes (only human coccyx bone) Ex. Hind limbs of a baleen whale and pelvic spurs on a python Speciation and Evolution can be Observed • Artificial selection • Speciation of fruit flies by divergence of host plant usage (ex. The apple maggot fly Rhagoletis) • Evolution of herbicide, pesticide, and antibiotic resistance Evidence that species are related: geographic continuity • Early scientists observed that extinct fossil species are typically succeeded in that same region by similar living species • Darwin and Wallace interpreted this as evidence that extinct forms and living forms are related, that they represent ancestors and descendants Ex. Geographic relationships: four mockingbird species on Galapagos islands -mockingbird species in the Galapagos are more closely related to each other than any is to a species from the mainland • the geographic distributions of Mammals also reflect their phylogenetic history Genetic and Developmental Homology Homology: similarity that exists in species that was inherited from an ancestor Genetic Homology: similarity among species in NDA sequences, gene content, or other genetic attributions that is due to shared ancestry Developmental Homology: similarity among species in embryonic traits that is due to shared ancestry Gene Homology • an identical/almost identical system is used by all known organisms to store the sequence of amino acids in proteins in nucleotides • plasma membrane • transcription of DNA, translation of RNA • use of ribozymes and ATP Homology: Similarity that exists in species that was inherited from a common ancestor Three main types of Homology • Genetic Homology • Development Homology • Structural Homology Genetic Homology: • Identical or almost identical system is used by all organisms to store sequences of • Eyeless and Anirdia influence where eyes are located in fruit flies and humans respectively • Presumable both are derived from an ancestral gene with the same places even though humans and fruit fly’s eyes are different Amino Acids in proteins in nucleotides • Chimp’s and human’s DNA is ~1.5% different • Plasma Membranes in cells Development Homology: • Identical or almost identical system is used during embryotic development between different organisms • Eye location gene in fruit flies and in human is only six amino acids different • Manipulation of this gene can cause eye development in fruit flies in different places (antenna, legs, etc…) • In embryotic stage, many animals develop gill pouches that disappear (except in fish and other water-breathing organisms) Ex. Branchial Cleft Cyst: congenital epithelial cyst that is derived from the branchial arches that are normally reabsorbed during embryonic development In fish, these arches turn into gills Structural Homology: • Identical or almost identical structural development of different organisms • Many animals have similar bone placements/structures • Toxins and allergins may similarly affect other species (or cell culture) and allow us to identify problems before (or after) problems experimentally arise in humans • Medicines can be tested in other species because mechanisms of action are homologous • Biological function in humans can be inferred from homologous function in other species Evidence for evolution • Fossils • Extinction (ancient DNA) • Transitional forms • Vestigial traits • Speciation and adaptation in real time • Geographic, temporal, and phylogenetic continuity/consistency • Genetic homology • Developmental homology • Structural homology Natural Selection: How it works • Individuals in a population vary in their traits (variation) • Some of these trait differences are heritable, meaning they are passed on to offspring (heritability) • In each generation, not all individuals reproduce the same amount and/or not all offspring survive (fitness effect and competition) Ex. Rhinobeetle • Individuals with certain heritable traits are more likely to survive and reproduce • Natural selection is one of the processes that determines whether individuals with certain traits produce more offspring than do individuals without those traits • Evolution can also be thought of as a change in allele frequencies in a population over time • Certain heritable traits allow organisms to survive better and are passed on to the next generation Ex. Assume a species of moth can be either dark or light coloured. This is controlled by two alleles Allele A1 (Recessive/Light) A2 (Dominate/Dark) Distribution in population before 50% 50% • If each moth is randomly assigned two alleles, most will be dark coloured • If a bird comes along and eats mostly black coloured moths, more light coloured moths will pass on their genes (more A1 alleles in population) Allele A1 (Recessive/Light) A2 (Dominate/Dark) Distribution in population after 62.5% 50% Bacteria Antibiotic Resistance • Sanitation, nutrition, and antibiotics (rifampin) greatly reduced deaths due to TB in industrialized nations form 1950-1980s • However, in the late 1980s, rates of TB started to surge due to the evolution of drug-resistant strains • DNA from rifampin-resistant bacteria was found to have a single mutation in a gene called rpoB that encodes a component with bacterial RNA polymerase • Rifampin works by interfering with bacterial RNA polymerase, but the mutation in the rpoB gene prevents • rifampin from interfering with this protein in the bacteria. • Under normal conditions, the mutant form of RNA polymerase does not work as well as the normal form • However, during antibiotic therapy with rifampin, bacteria cells with normal RNA polymerase grow more slowly or die, but those with mutant RNA polymerase proliferate • Mutations in genes can cause resistance to antibiotics in bacteria Alleles that confer Drug Resistance • The initial bacteria population was polymorphic • A strain existed that was resistant to the antibiotic • This strai
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