NATURAL SELECTION It is the process by which heritable traits that increase an organism’s chances of survival and reproduction are favoured over less beneficial traits. Originally proposed by Charles Darwin, natural selection is the process that results in the evolution of organism.

Points to remember about Natural Selection Populations evolve, but individuals do not. I.E., Natural selection acts on the level of the individual, but populations are the smallest unit that can evolve. Natural selection only works on heritable variations, not acquired traits. Natural selection can only work with what it’s given. Variations are produced by different genetic mechanisms. Natural selection is situational to a given environment in a given time and place. No ideal organism. Fitness of a given trait changes.

Natural selection Teacher notes This five-stage sequence examines natural selection among a population of different coloured rabbits. Suitable prompts could include: These rabbits look different. Could natural selection happen if every member of the rabbit population was identical? What's the key thing the rabbits have to be able to do to make sure their genes are passed on to the next generation? What might prevent a rabbit living long enough to reproduce? Which of these rabbits looks best adapted to their icy environment? How is the number of white and brown rabbits likely to change in the future?

Survival of the Fittest Reproduction is a very wasteful process. Animals and plants always produce way more offspring than the environment can support. Why? Fruit flies produce 200 offspring every 2 weeks!

Survival of the Fittest Individual species show lots of variation because of the different genes they inherit Only the offspring with the genes best suited to their habitat will stay alive and breed successfully. Many animals produce lots and lots of offspring to ensure that at least some (the fittest ones) will survive and pass on their genes.

True or false? Teacher notes This true-or-false activity could be used as a plenary or revision exercise on natural selection, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.

The mechanism of natural selection Teacher notes This ordering activity could be used as a plenary or revision exercise on natural selection. Mini-whiteboards could be used to make this a whole-class exercise.

Genetic Drift: random changes in allele (and genotype) frequencies from generation to generation due to sampling error

Bottleneck Effect Catastrophic change in allele frequency due to an outside factor. E.g: Disease Weather Environment Changes New Predators

Genetic Drift, part A: The bottleneck effect “Alleles” in original population “Alleles” remaining after bottleneck

Bottleneck effect Cheetah www.petsdoc.com/pics/funpages/ wildlifephotos/cheetah.jpg

Northern Elephant Seal Bottleneck Effect http://www.icsi.berkeley.edu/~dbailey/gallery/image/elephant.jpg Reduced to 20 individuals in 1896 Now 30,000 individuals, with no detectable genetic diversity

Genetic Drift, Part B: The founder effect • Change in allele frequencies when a new population arises from only a few individuals e.g., only a few fish are introduced into a lake e.g., only a few birds make it to an island

A Human Founder Event The Population of the Mountain Village of Salinas in the Dominican Republic Was 4,300 in 1974. The Village Was Founded By A Handful of People 7 Generations Before One Founder, Altagracia Carrasco, Had Many Children by Four Women The Alleles Carried by Him Were Therefore in High Frequency in the Founder Population Gene Pool Subsequent Population Growth Reduced the Force of Drift But “Freezes In” The Allele Frequencies Created by the Initial Founder Event So His Alleles Remain In High Frequency Even Today

Gene Flow • addition or removal of alleles due to individuals entering or leaving a population from another population EMMIGRATION IMMIGRATION