Evolutionary Mechanisms Chapter 15 Pages

Warm-up Question According to the theory of natural selection, why are some individuals more likely than others to survive and reproduce? According to the theory of natural selection, why are some individuals more likely than others to survive and reproduce? A. They pass on to their offspring new characteristics they acquired during their lifetime. B. They are better adapted to exist in their environment than others. C. They tend to produce fewer offspring than do others in the same environment.

Adaptations The heart of Darwin’s Theory of Natural Selection The heart of Darwin’s Theory of Natural Selection –Organisms adapt to their environment through slow change over time. –Variations in genes give rise to adaptations. adaptations – traits that help organisms survive in the environment in which they live. adaptations – traits that help organisms survive in the environment in which they live. Fitness – a measure of the contributions an individual trait makes to the survival of the next generation. Fitness – a measure of the contributions an individual trait makes to the survival of the next generation.

Environments Change Peppered Moths Example Peppered Moths Example Mid 18 th century = England’s industrial revolution resulted in tons of soot deposited on trees and rocks. Mid 18 th century = England’s industrial revolution resulted in tons of soot deposited on trees and rocks. The discoloration camouflaged dark colored moths. The discoloration camouflaged dark colored moths. Where these dark colored moths were once the minority, they are now the majority. Where these dark colored moths were once the minority, they are now the majority.

Types of Adaptation 1. Camouflage – allows organisms to become almost invisible to predators. (cuttlefish)

2. Mimicry – a species evolves to resemble another species. Often increases an organisms fitness because the harmless species looks like the harmful one so predators will stay away. Often increases an organisms fitness because the harmless species looks like the harmful one so predators will stay away.

5 Mechanisms of Evolution: 5 Mechanisms of Evolution: 1. Natural selection – is not the only mechanism of evolution 2. Genetic Drift Founder EffectFounder Effect BottleneckBottleneck 3. Gene Flow 4. Nonrandom Mating 5. Mutations Population Genetics

The Gene Pool Gene Pool – all of the genes present in a population Gene Pool – all of the genes present in a population Sources of Variation in a Gene Pool: Sources of Variation in a Gene Pool: 1. Two copies of chromosomes present in each cell 2. Mutations create new alleles 3. Other events cause a shuffling of genes into different combinations: a. crossing over b. random assortment (see next slide) c. and fertilization

Random Assortment

Breeding Bunnies Activity Today Work in PAIRS! NO MORE THAN 2!!! Work in PAIRS! NO MORE THAN 2!!! 50 red beans 50 red beans 50 white beans 50 white beans 1 large container for breeding 1 large container for breeding 1 waste container for the alleles of dead 1 waste container for the alleles of dead bunnies  bunnies  Instruction Sheet Instruction Sheet Data Sheet and Discussion Questions Data Sheet and Discussion Questions Graph Paper Graph Paper

Population Genetics Hardy & Weinberg (1908) – showed that evolution will not occur in a population unless allelic frequencies are acted upon by forces that cause change. Hardy & Weinberg (1908) – showed that evolution will not occur in a population unless allelic frequencies are acted upon by forces that cause change. Hardy-Weinberg Principle – when allelic frequencies remain constant, a population is in genetic equilibrium. Hardy-Weinberg Principle – when allelic frequencies remain constant, a population is in genetic equilibrium.

Hardy-Weinberg Principle Conditions – Equilibrium exists and evolution does not occur if: Population is very large Population is very large No immigration or emigration No immigration or emigration Mating is random Mating is random Mutations do not occur Mutations do not occur Natural selection does not occur Natural selection does not occur Populations rarely meet these requirements for long periods of time.

Hardy-Weinberg Equation Each genotype has two alleles, p and q. (p + q) 2 = 1 p pq + q 2 = 1 pq p q

Genetic Drift Any change in the allelic frequencies in a population that is due to chance. Any change in the allelic frequencies in a population that is due to chance. In large populations, enough alleles “drift” to insure that the allelic frequency of the entire population remains relatively constant from one generation to the next. In large populations, enough alleles “drift” to insure that the allelic frequency of the entire population remains relatively constant from one generation to the next. In smaller populations, however, the effects of genetic drift become more pronounced, and the chance of losing an allele becomes greater. In smaller populations, however, the effects of genetic drift become more pronounced, and the chance of losing an allele becomes greater.

Two Kinds of Genetic Drift: 1. The Founder Effect (an extreme example of genetic drift) -Can occur when a small sample of a population settles in a location separated from the rest of the population. -Example: Amish and Mennonite communities in the U.S. have a high frequency of six-finger dwarfism.

2. Bottleneck (another extreme example of genetic drift) Occurs when a population declines to a very low number and then rebounds. Occurs when a population declines to a very low number and then rebounds. The gene pool of the rebounded population now has reduced diversity. The gene pool of the rebounded population now has reduced diversity.

Gene Flow The random movement of individuals between populations (migration) increases genetic variation within a population and reduces differences between populations. The random movement of individuals between populations (migration) increases genetic variation within a population and reduces differences between populations.

Nonrandom Mating Usually, organisms mate with individuals within close proximity. This promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits. Usually, organisms mate with individuals within close proximity. This promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits.

Mutation A random change in genetic material A random change in genetic material Provides the raw material upon which natural selection works: Provides the raw material upon which natural selection works: –Occasionally, a mutation provides an advantage to an organism. This mutation will then be selected for and become more common in subsequent generations.

Natural Selection Acts to select the individuals that are best adapted for survival and reproduction. Acts to select the individuals that are best adapted for survival and reproduction. Acts on an organism’s phenotype and changes allelic frequencies in four ways: Acts on an organism’s phenotype and changes allelic frequencies in four ways: 1. through Stabilizing Selection 2. Directional Selection 3. Disruptive Selection, and 4. Sexual Selection

1. Stabilizing Selection:

2. Directional Selection:

3. Disruptive Selection:

4. Sexual Selection Males are larger and more colorful than females. Males are larger and more colorful than females. Brighter colors and bigger bodies enhance reproductive success. Brighter colors and bigger bodies enhance reproductive success. player/animals/birds- animals/seabirds/boobies_bluefooted.html z9Y3k&safety_mode=true&persist_safety_ mode=1&safe=active

Speciation When some members of a population become separated from the group and change so much that they can no longer mate with members of the original population. 2 Types: 1. Allopatric Speciation 2. Sympatric Speciation

1. Allopatric Speciation The most common form of speciation The most common form of speciation A physical barrier divides a population into two (or more) populations. Over time, the populations will change until eventually they are no longer able to breed with one another. A physical barrier divides a population into two (or more) populations. Over time, the populations will change until eventually they are no longer able to breed with one another.

2. Sympatric Speciation When a species evolves into a new species without a physical barrier. When a species evolves into a new species without a physical barrier. Occurs most commonly among plants through polyploidy (a mutation that increases a plant’s chromosome number). Occurs most commonly among plants through polyploidy (a mutation that increases a plant’s chromosome number).

Patterns of Evolution 1. Adaptive Radiation 2. Coevolution 3. Convergent Evolution

1. Adaptive Radiation Also called divergent evolution Also called divergent evolution Can occur in a relatively short period of time. Can occur in a relatively short period of time. When one species gives rise to many in response to the creation of a new habitat or another ecological opportunity. When one species gives rise to many in response to the creation of a new habitat or another ecological opportunity. Example = cichlid fishes Example = cichlid fishes

2. Co-evolution Many species evolve in close relationship with other species. Many species evolve in close relationship with other species. The evolution of one species can affect the evolution of another species. The evolution of one species can affect the evolution of another species. Example = comet orchids and the moths that pollinate them. The foot-long flowers of this plant perfectly match the foot-long tongue of the moth. Example = comet orchids and the moths that pollinate them. The foot-long flowers of this plant perfectly match the foot-long tongue of the moth.

3. Convergent Evolution When unrelated species evolve similar traits even though they live in different parts of the world. When unrelated species evolve similar traits even though they live in different parts of the world. Occurs in environments that are geographically far apart but that have similar ecology and climate. Occurs in environments that are geographically far apart but that have similar ecology and climate.

Example for convergent evolution: