Genetics and Evolution

Genetics and Evolution Populations evolve, NOT individuals! Evolution = changes in a population’s genes over time

Vocabulary Gene pool = a collection of all of the possible genes in a population Allelic frequency = the % of an allele in a gene pool   Genetic equilibrium = occurs when allele frequency does not change (NO EVOLUTION!)

Genetic equilibrium So what are some ways that the genetic equilibrium changes? 1. mutation most mutations are lethal and those organisms do not survive occasionally a mutation results in a useful variation and the new gene is selected for

Genetic equilibrium So what are some ways that the genetic equilibrium changes? 2. genetic drift chance events alter the gene pool usually affects smaller populations Ex. Amish population of 12,000 carries a recessive allele that results in short arms and legs and extra fingers and toes

Genetic equilibrium So what are some ways that the genetic equilibrium changes? 3. migration - transport of genes to and from a population

Genetic equilibrium So what are some ways that the genetic equilibrium changes? 4. natural selection most significant effect on genetic equilibrium

Natural Selection can Change the Genetic Equilibrium in 3 Ways

Changes in genetic equilibrium 1. Stabilizing Selection: favors the average form of a trait results in less variation in a population Ex: average sized spiders

Changes in genetic equilibrium 2. Directional Selection favors one extreme form of a trait results in species showing one extreme form of a trait Ex: woodpeckers with long beaks

Changes in genetic equilibrium 3. Disruptive Selection favors both extreme forms of a trait can result in 2 new species over a long period of time Ex: light and dark limpets

Evolution of a new species Speciation = the evolution of a new species (when interbreeding is prevented)

What leads to speciation? 1. Geographic isolation EX: Tree frog population with a river separating them

What leads to speciation? 2. Reproductive isolation EX: Genetic- genetic material becomes so different that fertilization can’t occur EX: Behavioral- one pop of frogs mates in the fall, the other in the spring

What leads to speciation? 3. Change in chromosome number (polyploidy) EX: nondisjunction occurs during meiosis leaving the zygote (4n) instead of 2n; wheat, cotton, and apples are examples Only takes one generation to create a new species

Speciation rates 1. Gradualism: a new species forms through a gradual change of adaptations 2. Punctuated equilibrium a new species forms quickly in bursts, with long periods of genetic equilibrium in between; 10,000 years or less

Patterns of evolution 1. Adaptive radiation: an ancestral species evolves into a wide variety of species to occupy their own niche or diverse habitat EX: honeycreepers on the Hawaiian Islands EX: Darwin’s finches on the Galapagos Islands

Patterns of evolution 2. Divergent Evolution: species that were similar become different in order to adapt to different environments (Adaptive radiation is a type of divergent evolution)

Patterns of evolution 3. Convergent Evolution : species that were unrelated evolve similar traits in order to occupy similar environments in different parts of the world EX: pipe cactus and Euphorbia – both have fleshy body type and no leaves to survive the desert but totally unrelated