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Chapter 11: The Evolution of Populations Mechanism for Evolution video Darwin stated that in a population there are variations • Population: – All the individuals of the same species in a given area. • Gene pool – The combined alleles (different form of the gene individuals in a population – Individual members of a population contribute their alleles to a common pool of genes. On an island, there are 7 boars. 2 are pure for the long bristles gene (BB), 3 are hybrids (Bb) for long bristles and 2 are pure recessive (bb) for short bristles. What is the likelihood of either allele (B or b) showing up in the next generation? • Allele frequency: – Measure of how common an allele is in the population – The likelihood of that allele showing up in the population. How about something closer to home? Let’s look at the allele frequency for colorblindness in our classroom. # of “N” “n” alleles # of colorblind individuals = _____ # of carrier females = ____ # of homozygous dominant females = ___ # of normal males = ___ ____ ____ ____ ____ Normal allele ____ ____ Colorblind allele ____ Total # of alleles ____ Allele frequency Normal ____ Colorblind ____ ____ Population Genetics Problems In a village, there are 20 people who do not have a gene for Sickle Cell Anemia, 10 who are carriers of the trait and 3 who have Sickle Cell Anemia a) Calculate the: • Phenotype frequencies for the trait • • • • % NN % NS % SS Allele frequencies for normal RBC and Sickled RBC. • N S Changes in allele frequency within a gene pool can be caused by a number of factors 1. Gene Flow • • • • The movement of alleles from one population to another Migration of organisms into and out of the population Increases the genetic variation of the receiving population and decreases the variation of the other population. A lack of gene flow will lead to Speciation, the formation of different species. Bad luck for the reds & where are the yellows?!! Some sorter didn’t do their job!! Did natural selection play a part in the loss of variation in the beetle population or was there another factor not related to natural selection? 2. Genetic Drift • In a small population (isolated one), a particular allele may occur more or less frequently even though it was purely due to chance. • Leads to loss of variation in a population Among the Amish population, polydactylism is very common. Why? Is it a favorable trait for working on farms & doing more “hand work”? Animation Sicilian family An Australian Aboriginal cave painting What would happen to the population of frogs illustrated below, in the next generation 3. Bottleneck effect – Effect of a destructive event that leaves a few survivors in a population – Form of Genetic drift Why is a peacock have such impressive feathers? 4. Sexual Selection – – – – Certain traits increase the likelihood of finding a mate and therefore, passing on your genes (making you fitter!) Since females need to be selective with their limited number of eggs, she wants to be certain that she selects the correct male who will increase the chances of having the fittest offspring. Why the peacock (male) is so brightly colored Compare the male to the female cardinal Mechanism for Evolution video The story of the fruit flies 1. 2. 3. 4. A bunch of flies were minding their own business feeding on bananas Suddenly, a hurricane washed the bananas & flies onto another island Since conditions & food are different on the new island, the flies evolve separately from their mainland relatives When some of the flies mix with the mainland relatives, they can no longer produce viable offspring when they mate. Speciation has occurred!! New island Mainland Mainland Look at the illustration above and discuss what might have happened. The original population was beige in color. They were feed different types of food, one high in starch and the other high in maltose which caused variations in the coloration, resulting in light variations and the darker variations of flies The light flies only mated with the light colored flies and the darker flies only mated with the darker flies, eventually resulting in two separate species Reproductive isolation Occurs when members of different populations can no longer mate and produce successfully with each other. Predict what will happen. Geographic isolation – A physical barrier such as a river, mountain, valley, … separates two populations resulting eventually in reproductive isolation with the formation of new species. – Most common form of isolation – Isolated populations become genetically different over time Geographic Isolation Animation Watch the videos of mating dances for a ruffed grouse, a peacock and a fiddler crab • Ruffed Grouse courtship display. – YouTube • https://www.youtube.com/watch?v=Hgh7nhG zNUk • https://www.youtube.com/watch?v=jTBHiZtn CsA • https://www.youtube.com/watch?v=yCn6g3p Xc1s • http://www.pond5.com/stockfootage/733488/giraffes-tussle-and-fightdisplay-mating-behavior.html Behavioral isolation Isolation caused by differences in courtship or mating behaviors – Different chemical scents, dances, songs and signals Adaptive Radiation • Rapid evolution of many diverse species from ancestral species • Our beak activity showed this. • Organism diverge based on their variation to fill a niche that matches their variation.