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Transcript
Ch 23 Mechanisms of Evolution - Which one would not promote change over time? Natural Selection a major mechanism for evolution Which organisms will be selected, depends on their direct ability to survive & reproduce What’s the premise of Natural Selection - coined by Charles Darwin… 1. There is a struggle for existence Organisms must compete for limited resources - food, space, a mate. 2. Many more offspring are born each season than can possibly survive to maturity (overpopulation) 3. Their survival is based on beneficial phenotypes (inherited adaptations) that give them an advantage, increasing their likelihood of survival and production of more viable offspring. 4. Alleles (variations of a trait) tend to increase over time when “selective pressure” favors that phenotype. 5. Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species Which premise do these photos demonstrate? What is the selective pressure ? – and what allele or phenotype is favored in each photo? Survival of The Fittest Rank these apes by fitness level (#1 being the best) Justify your rationale. What is the selective pressure? Name Boris Rex Hank Abe Age at Death 13 years 12 years 16 years 10 years # offspring fathered 18 20 25 20 # offspring surviving into adulthood 15 14 14 19 Size 6’2” 5’8” 5’10” 5’8” Which premise do these photos demonstrate? Advantages/Disadvantages of each and compare. Emperor Scorpion r/K Selection - Quality vs Quantity - at parental expense Thornbug Treehopper Variation (key to evolution) - comes about in two ways 1. Sexual reproduction creates variation causes recombination of alleles into new arrangements in every offspring Genetic shuffling is a source of variation 2. Mutation creates variation new mutations are constantly appearing not all bad) causes changes DNA sequence (change amino acid sequence? -- protein? -- phenotype? -- fitness??) Some fish adapt by evolving antifreeze proteins. (…and it’s Princess Diana, Prince William & Harry Jonas Brothers Baldwin Brothers Venus & Serena Reproduction recombines alleles into new arrangements in every offspring Madonna & daughter Luke & Owen John Lennon’s sons Cameron & Chimene Diaz Penelope Cruz Martin Sheen and sons Kennedy’s Mariska Hargitay & mom What are the beneficial phenotypes? What “drives” the phenotype? What is the selective pressure that ensures these alleles are kept in the population? Predatory Selection Defensive adaptation Predatory Selection Cryptic Coloration (camouflage) Magnificent Frigatebird Sexual Selection - desire to mate Physiological Selection - desire to survive in their environment In a Directional Selection, the shift in the population is against one extreme variant toward a preferred extreme the longer neck giraffes are more physically fit and have a better chance of survival and reproduction rate than do the medium or smaller giraffes. What is being selected against? What is being selected for? What’s the selective pressure? Natural selection can act in a number of directions Use one animal from your illustrative examples to create a Title and In a Directional Selection, the identify the Independent & Dependent shift in the population is variables on the x & y axes against one extreme variant toward a preferred phenotype What is being selected against? What is being selected for? What’s the selective pressure? In a Stabilizing Selection, the shift in the population is toward the moderate variant this graphs shows that the two extremes have been reduced in the population, and the medium sized lizards have the best chance at survival & reproduction. What is being selected against? What is being selected for? What’s the selective pressure? Natural selection can act in a number of directions Use one animal from your illustrative examples to create a Title and In a Stabilizing Selection, the identify the Independent & Dependent shift in the population is variables on the x & y axes toward the moderate variant against/eliminating both extremes What is being selected against? What is being selected for? What’s the selective pressure? In a Disruptive Selection, the shift in the population is against the mean/middle selecting for toward both extremes - this graphs shows that the two extremes have been extenuated in the population, those birds with either long beaks or really short beaks have the best chance at survival & reproduction. What is being selected against? What is being selected for? What’s the selective pressure? Natural selection can act in a number of directions Use one animal from your illustrative examples to create a Title and In a Disruptive Selection, the identify the Independent & Dependent shift in the population is variables on the x & y axes selection against the mean, toward both extremes What is being selected against? What is being selected for? What’s the selective pressure? Changes in populations Evolution of populations is measuring changes in allele frequency all the genes & alleles in a population = gene pool Factors that alter allele frequencies in a population are: 1. natural selection - survival of the fittest 2. genetic drift - evolution is also driven by random, chance events a. founder effect - small group splinters off to start a new colony b. bottleneck effect - some factor (usually a disaster) reduces a population to a small number, then it recovers and expands again. 3. gene flow - immigration and emigration allow for the movement of genes, creating a more diverse gene pool Looking at the following pictures, which factor has created a change in the allele frequencies b. Gene flow Population spread over large area migrations = individuals move from one area to another sub-populations may have different allele frequencies Migrations cause genetic mixing across regions = gene flow new alleles are moving into gene pool reduce differences between populations Genetic Drift - as per Founder Effect What is this allele frequency? Some individuals from an original population break away, find a new place and start their own colony - they survive and reproduce Record the allele frequencies for each population. Descendants A Founder A Founder B What is this allele frequency? Descendants B What is this allele frequency? Genetic Drift - as per Bottleneck Effect When large population is drastically reduced by a disaster famine, natural disaster, loss of habitat… loss of variation by chance alleles lost from gene pool reduces variation reduces ability to adapt puts populations at risk Any Questions?? https://www.superteachertools.net/speedmatch/speedmatchfromj.php?gamefile=1392690776#.U-Yryig9U1c