Natural selection powerpoint

SBI-3U January 31st, 2011 Kyla Bond Evolution: Natural Selection The result of natural selection over time First observed by Charles Darwin Theory based on 5 observations: Heritable Variation within populations Limiting resources Stabilization More offspring than adults What is Evolution? 5 observations led him to believe: Certain traits would allow individuals in a species to have greater survival Individuals within a population compete for resources Result that over generations, the population of individuals with the “better” genes will be dominant Charles Darwin Definition: Nature favours the survival of some individual within a species over others (within a population) Genetic variation required Results from genetic mutations and recombination Genetic variation: A population that has differing alleles at the same location (locus). i.e. eye colour Genetic mutation: Changes in the structure of a gene. Recombination: The switching of genes between chromosomes (from the same locus on each chromosome) Natural Selection As a result of natural selection, individuals possessing a specific trait are more successful than others possessing a different trait “Survival of the fittest” Think of as many factors that may result in natural selection Climate Food availability Shelter Predators Mate availability Think-Pair-Share Natural Selection Example http://phet.colorado.edu/en/simulation/natural-selection Directional Selection Stabilizing Selection Disruptive Selection Sexual Selection Types of Selection Directional Selection Stabilizing Selection Disruptive Selection Sexual Selection Types of Selection One of the extreme traits are favoured Shift away from average traits Common in artificial breeding Selection of fruits and vegetables Directional Selection Darwin’s Finches Example of directional selection Initially finches with medium sized beaks Eat medium-sized seeds Plants available had large and some medium seeds Carrying capacity was reached (limited by seeds available) New hatchling exhibited genetic variation Those capable of eating the large seeds had greater survival No competition for food Since large-beaked birds are healthier they are more likely to reproduce Shift towards the extreme trait of a larger beak Beaks!-Illustration Tool Simulate a beak 4 different sized objects Act as seeds Container Acts as stomach Use the “beak” to pick up as many of the “seeds” as possible and place them in the birds “stomach” How many seeds were you successfully able to pick up? Directional Selection Stabilizing Selection Disruptive Selection Sexual Selection Types of Selection Opposite of directional selection Average traits are favoured Selection away from extreme traits Reduces genetic variability Stabilizing Selection Example of stabilizing selection Newborns of average weight(6-8lbs) have a much higher survival rate than those far above or below Birth Weight Directional Selection Stabilizing Selection Disruptive Selection Sexual Selection Types of Selection Both end of the extreme traits are favoured Two phenotypes favoured Shift away from the average traits (similar to directional) Increases genetic variation within the population May result in speciation over time Disruptive Selection Directional Selection Stabilizing Selection Disruptive Selection Sexual Selection Types of Selection Reproductive success favours individuals with certain traits over others Usually results in sexual dimorphism Sexual dimorphism: Differences between male and females of the same species Colouration, size, physical alterations (i.e. antlers),etc. Sexual Selection 2 types : Male-male competition “intrasexual” Female choice “intersexual” Male-male competition- males compete over territory in which the females are located Cost for the males-although some males are very successful, other may never pass on their genes Female choice- females choose males based on their appearance and behaviours Acts as sign of good health Cost for the males- bright colouration may attract predation Bird of paradise http://www.youtube.com/watch?v=7dx2CUMtZ-0&feature=fvsr Elephant seal fighting http://www.youtube.com/watch?v=viBalOK9nMs&feature=related Sexual Selection Videos NO! Is Natural Selection Necessary? Change in gene pool of a population as a result of chance Difference? Greater influence on smaller populations Types of genetic drift: Bottleneck effect Founder effect Genetic Drift Loss in genetic variation due to a large reduction in population size Likely to result in genetic drift Loss of rarer genes May occur due to hunting or loss of habitat.. Bottleneck Effect When individuals leave the original population and create a new smaller population Rare allele could become common in the new population Gene pools will differ Founder Effect Red was initially dominant in the population After the founder effect, blue is now dominant Original Population New Population Describes the relationship between allele frequency within a population and the likelihood of it remaining constant Any factor resulting in a change in allele frequency? Evolution Conditions for evolution: Natural selection Genetic drift Mutations Immigration and emigration Horizontal gene transfer Hardy-Weinburg Principle Humans have a large impact on evolutionary change How? Humans and Evolution Natural selection is the primary route of evolution Genetic variation required for natural selection 4 types of selection; Disruptive Stabilizing Directional Sexual Genetic drift may also cause evolutionary change Much quicker in smaller populations Lesson Recap Biology 11U. 2011. Nelson. Pg.304-35. http://staff.tuhsd.k12.az.us/gfoster/standard/birdbeakdatatable.htm http://en.citizendium.org/wiki/Horizontal_gene_transfer http://www.biology-online.org/2/11_natural_selection.htm  http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_25 References