Evolution of Populations Population Genetics Natural Selection nature

Evolution of Populations

Population Genetics Natural Selection: nature selects which individuals survive and reproducen Evolution: occurs as a populations genes and their frequencies change over time n Gene Pool: all the genes of a population n

Population Genetics n If the frequency of the alleles doesn’t change over time, the population is at genetic equilibrium

Population Genetics w When alleles are brought in and out of a population due to migration of individuals, it is called gene flow. methemoglobinemia

Population Genetics w Gene frequencies in a population can change due to natural selection w 3 types of Natural Selection Stabilizing Selection: natural selection favors the average individuals in the population l It is best to be average! l Cactus with medium number of spines

Stabilizing Selection

Types of Natural Selection Disruptive Selectionnatural selection favors both extreme phenotypes of a trait in a population Its not good to be average! n Medium color limpets do not survive n

Disruptive Selection

Types of Natural Selection Directional Selection-natural selection favors one extreme phenotype of a trait in a population n It is best to be different! n Antibiotic resistant bacteria

Directional Selection

Practice n n n Which of the three selection types would result in black or white snuzzles but no gray ones? Which of the three selection types would result in medium colored snuzzle being the most frequent in the population rather than light or dark snuzzles? Which selection type might ultimately lead to two separate species unable to mate? Natural Selection Evolution in Action

Speciation w Natural selection changes the gene pool and leads to evolution of new species over time. w Speciation occurs when 2 populations of a species changed so much they can no longer interbreed and produce fertile offspring Hummingbird Speciation

Speciation is caused by: w Geographic Isolation n Physical barrier divides 2 populationsl Galapagos species, grand canyon squirrels

Speciation is caused by: w Reproductive Isolation n Physical or behavioral changes prevent 2 populations from interbreeding l One species of flower pollinated by bees, one by hummingbirds

Speciation is caused by: w Change in chromosome number n Polyploidy-mutation during meiosis resulting in multiple copies of chromosomes l Polyploids can then only mate with other polyploids

Speciation w Can occur rapidly n Punctuated Equilibrium w Can occur very slowly n Gradualism

Faces of Our Ancestors Patterns of Evolution Finding Lucy Walking Tall w Divergent Evolution: Species that once were similar or closely related become very different and more distinct.

Adaptive Radiation w A type of Divergent Evolution w One ancestral species evolves into a variety of species occupying a variety of habitats w Examples: n Galapagos finches n Hawaiian honeycreepers The Big Picture

Adaptive Radiation

Patterns of Evolution w Convergent Evolution: Due to similar environmental pressures unrelated organisms evolve similar traits n Penguin, dolphin, fish with same body shape