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ANTB15 reading one notes.docx

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Maydianne Andrade

ANTB15 – reading one and lecture 2 notes Big Picture on Evolution (issue 5 Jan 2007) “Nothing in biology makes sense except in the light of evolution” – Theodosius Dobzhansky (1973) when he said this he was referring to the link between genetics (Mendel 20 century) and evolutionary change (Darwin 19 century). Genetics is the mechanism, which allows natural selection to occur. Darwin’s Big Idea During the 19 century two naturalists, Charles Darwin and Alfred Russel Wallace independently came up with a theory to explain how evolution occurs. Their shared insight was that living species were not fixed, but were the product of a gradual process of change driven by natural selection: the survival and reproduction of organisms suited to their environment, at the expense of those less successful. Darwin published his ideas in his book On the Origin of Species by Means of Natural Selection Natural Selection 1. Organisms produce more offspring than survive to reproduce 2. Offspring vary slightly 3. Characteristics can be passed on from generation to generation 4. Those most suited to their environment survive at the expense of those less fit. Sexual Selection – a variation of natural selection (an animal may have a specific feature that may make them more vulnerable to predators yet that characteristic is favoured because it may attract females and in that case they can pass their genes to their offsprings. An example of this would be the coloured plumage of certain birds.) Definitions to know Genotype Genetic characteristic of an individual Phenotype The physical traits of an individual. Dependent on genotype and interactions with environment Allele A version of a gene. Many genes have a number of different alleles, owing to small variations in gene sequence Genome The complete set of genetic instructions of an individual or species Sexual Where an offspring’s genes come from two parents reproduction Asexual Where an offspring is genetically identical to its (single) parent reproduction 1 Cultures and their explanation for our existence Inuit – land rose from water and a raven (bird) stabbing its beak into it secured it Ancient Egypt – Ra arose from a blue lotus flower (interactions with water, air, darkness and eternity). Ra created a wife and had a son Caught in a drift Change is DNA (mutations) can be beneficial, harmful or have no difference (neutral change). Due to genetic drift the neutral changes in DNA are important. The frequency of alleles may fluctuate over time and cause evolutionary change. Due to human’s small founder population the changes in allele frequency probably had a huge impact on humans. Cultural Evolution Biological evolution acts through our genes. Culture is our systems of beliefs, values and knowledge, it is passed on through interactions between people. A strong cultural system is language. Heredity was a mechanism to explain natural selection however Darwin did not know about genes. Gregor Mendel carried out experiments (peas) that lay the foundation of genetics. Genes contain the hereditary information. Tree of life The idea that all living thing arose from a common ancestor has given rise to the analogy of the “tree of life”. There are three main groups: prokaryotes, eukaryotes and archaea (new finding) Genes are the units of inheritance and can be used to work out evolutionary relationships. Hox genes are found throughout the animal world and can be used to create fruit flies, cockroch, even human beings. Genes can take on a new function by mutations (change in DNA sequence). However mutations doesn’t necessarily change the protein, which the DNA encodes for. Loss of gene funtion may indicate that the gene is/has become inactive (pseudogenes). Speciation Species- a group of animals or plants that are able to interbreed (and produce fertile offsprings). New species arise when two populations of the species develop genetic changes to the point where they are unable to interbreed and produce fertile offsprings. This could occur when the population become geographically separated. Inter-species crosses mostly generate no viable offspring (chomosomal or genetic incompatibilities). Inter-species crosses can result in an offspring but that offspring will not be fertile (mule). 2 Pathogen evolution Bacteria’s advantage in the evolutionary sense is that they are able to reproduce within minutes and therefore they are able to spread rapidly. Bacteria can form mutations that can tolerate antibiotics (huge advantage) These drug resistant strains of ba
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