Mechanisms of Evolution

Evolution Changes in a population over time. Mechanisms of evolution (8) Mutations Gene flow Genetic drift Natural Selection (survival of the “fittest”) Artificial Selection Recombination Non-Random Mating Isolations (speciation)

Mutations Mutations are random changes in DNA, which if favorable, can be passed down from one generation to the next. These random mutations play an important role in evolution

Mechanism of Evolution: Mutations Original Population

Mechanism of Evolution: Mutations After Mutation

Mechanism of Evolution: Mutations Many Generations Later Make sure students compare the original population to the population many generations later. This will help them see how the population changed as a result of the mutation.

Gene Flow Genes move with individuals when they move (emigrate or immigrate) into and out of a population…and it changes the gene pool

Genetic Drift Genetic Drift – the random fluctuation due to chance occurrences alone It is more significant in smaller populations It increases the chance of any given allele becoming more or less prevalent when the number of individuals is small Ex.) Founder Effect and Bottleneck Effect

Section 15.1 Summary – pages 393-403 Natural Selection Natural selection is the idea that organisms with favorable/beneficial traits survive, reproduce, and pass those traits to the next generation “Survival of the Fittest”. ENVIRONMENTALLY CONTROLLED Organisms without these variations/traits are less likely to survive and reproduce. Section 15.1 Summary – pages 393-403

Section 15.2 Summary– pages 404-413 NATURAL SELECTION There are three different types of natural selection: stabilizing, directional, and disruptive. Stabilizing selection is a natural selection that favors average individuals in a population. Evolution will not occur Middle sized Siberian Huskies are selected for Section 15.2 Summary– pages 404-413

Section 15.2 Summary– pages 404-413 NATURAL SELECTION Directional selection occurs when natural selection favors one of the extreme variations of a trait. This type of selection can lead to rapid evolution of a population. Section 15.2 Summary– pages 404-413

Section 15.2 Summary– pages 404-413 NATURAL SELECTION In disruptive selection, individuals with either extreme of a trait’s variation are selected for. This results in eventually having no intermediate form of a trait, and leading to two separate species. Section 15.2 Summary– pages 404-413

Natural Selection Shifts to middle range 2 extremes 1 extreme

Section 15.1 Summary – pages 393-403 ARTIFICIAL SELECTION Breeding organisms with specific traits in order to produce offspring with ideal (Intentional breeding for certain traits) A Goldendoodle (Golden retriever/ Poodle) Section 15.1 Summary – pages 393-403

Recombination (Crossing over) As we learned in the genetics unit, CROSSING OVER leads to genetic material being shuffled. This shuffling, along with sexual reproduction, leads to variation within populations. This variation leads to selection, which ultimately leads to evolution. Locate an appropriate website or websites with real world examples of recombination and genetic shuffling. Possible websites to consider are the Berkeley Evolution website and the Learn Genetics Utah website. These online libraries have many resources which you may find appropriate for your students and district. Embed examples onto this slide.

The red coated birds traits are favored in choosing a mate Non-Random Mating Blue = BB or Bb Red = bb Original Population The red coated birds traits are favored in choosing a mate x Students may need to think about Punnett squares probability of offspring. It maybe helpful to do a cross between two heterozygotes and also two red individuals. This will show students that not only are red individuals all red offspring but blue individuals are also producing red offspring as well. Because of this and non-random mating, the frequency of red alleles will increase many generations later. Most species do not just mate randomly… there are desired or favorable traits that they look for when choosing a mate (ex..peacocks)

Many Generations Later Non-Random Mating Over time, you would see the favored traits more prevalent than the undesired traits. Many Generations Later

Reproductive Isolation Two ways reproductive isolation occur: Prezygotic mechanisms Geographic Temporal Mechanical Behavioral Postzygotic mechanisms Infertility

Section 15.2 Summary– pages 404-413 SPECIATION The evolution of new species, a process called speciation. This occurs when members of similar populations change so much from each other that they no longer interbreed to produce fertile offspring. Section 15.2 Summary– pages 404-413

Section 15.2 Summary– pages 404-413 SPECIATION In nature, physical barriers can break large populations into smaller ones. Geographic isolation occurs whenever a physical barrier divides a population and over time they change and become two different species. Reproductive isolation… Section 15.2 Summary– pages 404-413

Section 15.2 Summary– pages 404-413 SPECIATION without a physical barrier Some speciation occurs while the organisms still exist in the same area… Reproductive Isolation Behavioral, Temporal, Mechanical Section 15.2 Summary– pages 404-413

Speciation Northern Arctic Fox Spreads northward and Adapted to heat through lightweight fur and long ears, legs, and nose, which give off more heat. Adapted to cold through heavier fur, short ears, short legs, short nose. White fur matches snow for camouflage. Gray Fox Arctic Fox Different environmental conditions lead to different selective pressures and evolution into two different species. Spreads northward and southward separates Southern population Northern Early fox