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HOW does Evolution Occur? Evolution Evolution: The change of genetic information over time, from one generation to the next. • • • • Ingredients for Evolution “VIST” Variation mutations & sexual reproduction Inheritance DNA passes on traits Selection well matched or not to enviro choice of mates • Time not a choice, can take millions of years or happen relative quickly due to random events Mutations- achieve variation Mutation: cause variation in genes A change in the order of bases in DNA that creates a new version of a gene (an allele) 5 Mechanisms of Evolutionary Change: 1) 2) 3) 4) 5) Mutation Natural Selection Gene Flow Genetic Drift Non-Random Mating Natural Selection… “Survival of the Fittest” • Individuals with favorable traits: ( traits that are well suited for their environment) are more likely to survive & pass on their genes via offspring • Example: English peppered moth (Biston betularia) & the Industrial Revolution - light and dark phases Five Mechanisms of Evolution (Review from last class) 1. Mutation: Change in an organism’s DNA that creates a new allele. 2. Natural selection: Individuals well suited to their environment are more likely to survive Five Mechanisms of Evolution 3. Gene Flow: The gain or loss of alleles (versions of a specific gene) from a population by the movement of individuals – Immigration or emigration 4. Genetic drift: The occurrence of a chance/random event causes a particular version of a gene (a trait) to become more OR less common in a population the relative frequency of a gene changes due to chance! Implies that inheritance of traits is NOT ALWAYS related to fitness or natural selection… sometimes CHANCE is a factor! Examples of Genetic Drift: 1. Natural Disasters: Earthquakes, Volcanoes, Floods randomly wipe out part of the population Eg) short legged goats at bottom survive goats at top are killed, short leg gene gets passed on in a & becomes much more common! 2. Number of offspring - an individual with a unique trait (randomly) has more offspring than it’s sister. The unique trait becomes more common Ex) Dog A has 10 puppies- curly hair Dog B has 6 puppies- straight hair The allele for curly hair becomes more common because Dog A had more puppies not because it helps survival! • 3. Colonization: -a small number of individuals are separated and take over a new area (eg. An island) Ex) Darwin’s finches Different islands have finches with different beak types could have resulted from BOTH Genetic Drift AND Natural Selection Speciation: • The evolution of new species. • Often results from reproductive isolation! • populations are separated & become so different reproduction does not / cannot occur Adaptive Radiation • Introduction to new & diverse environments creates new “selection pressure”… – a new or different trait allows individuals to be well suited to their new environment – Over time this trait increases in frequency & can lead to speciation • Many different species come from one common ancestor • aka “Divergent Evolution” • Example: Darwin’s Finches Divergent Evolution in Darwin’s Finches QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Divergent Evolution in Darwin’s Finches QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Homologous Structures QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. • Result from adaptive radiation • Structures that may LOOK DIFFERENT & SERVE DIFFERENT NEEDS BUT originate from the same body parts Analogous Structures • Result from convergent evolution • Structures similar in appearance & function BUT have different origins & internal structure Convergent Evolution • Species from different evolutionary branches come to resemble one another if they live in very similar environments. • Example: 1. Ostrich (Africa) and Emu (Australia). 2. Sidewinder Snake (Mojave Desert) and Horned Viper (Middle East Desert) Two Theories of How New Species Arise 1. Gradualist Model (Darwinian): Slow changes in species over time. 2. Punctuated Equilibrium: Evolution occurs in spurts of relatively rapid change. A B Review from last class… How do New Species Arise? 1. Gradualist Model (Darwinian): Slow changes in species over time. 2. Punctuated Equilibrium: Evolution occurs in spurts of relatively rapid change. Five Mechanisms of Evolution 5.Non-random mating: The selection of mates other than by chance. • “Sexual Selection” • Video to illustrate • (8mins) Does Sex Matter? • Yes! • Evolution can be driven by mate choice and pressure to attract mates • Mating is NOT random…it creates a “selection pressure” • Sex = “an evolutionary arms race” 5. Non-random mating: The selection of mates other than by chance. • Video: “Why Sex?” (~8 mins) Results of Sexual Selection • Males: competition • Males are often selected for increased size for fighting other males, defending territory etc in order to obtain access to females • Females: choice of mates • “Handicap Principle”- females are attracted to males with potentially damaging traits (ie bright colours) because it advertises “good genes” ie) ability to be colourful and still avoid predators