Review Questions:   1. What are the 5 evidences for Evolution? 2. What is the difference in Homologous, Analogous and Vestigial Structures? 3. What does Fitness and Adaptation mean?   4. What are the 4 main principles of The Theory of Natural Selection?

1. What are the 5 evidences for Evolution 1. What are the 5 evidences for Evolution? The 5 evidences for evolution are: 1. Fossil Record 2. Comparative Embryology 3. Comparative Anatomy 4. Comparative Biochemistry and DNA 5. Direct Observations

Review Continued 2. What is the difference in Homologous, Analogous and Vestigial Structures? Homologous structures have features that are similar in structure, appear in different organisms and have different functions. Analogous structures are structures that perform a similar function but are not similar in origin. Vestigial structures are remnants of organs or structures that had a function in an early ancestor.

3. What does Fitness and Adaptation mean? Fitness the ability to survive and produce more offspring of a population in a given environment. Adaptation are variations that allow some individuals to survive better than others

Review 4. What are the 4 main principles of The Theory of Natural Selection? 1. Variations 2. Overproduction 3. Adaptations 4. Descent with Modification

Chapter 16: The Evolution of Populations

Genetic Variation Within Populations Words to Know: Gene Pool, Allele Frequency, Phenotype, Gene, Allele, Meiosis, Gamete

Genetic Variation Natural selection acts on different phenotypes in a population. In order to have different phenotypes, a population must have genetic variation. A population with a lot of variation likely has a wide range of phenotypes. Genetic Variation is stored in a population’s Gene Pool – the combined alleles of all of the individuals in a population. An Allele Frequency is a measure of how common a certain allele is in the population. What is the relationship between allele frequencies and a gene pool?

Genetic Variation Comes from Several Sources Mutation A mutation is a random change in the DNA of a gene. This change can form a allele. If these changes are in reproductive cells they can be passed on to new generations.

Genetic Variation Comes from Several Sources Recombination New allele combinations form in offspring through a process called recombination. Most recombination occurs during meiosis in crossing over. This shuffling results in many new combinations.

Natural Selection in Populations Words to Know: Normal Distribution, Microevolution, Directional Selection, Stabilizing Selection, Disruptive Selection, Natural Selection.

Natural Selection Acts on Distributions of Traits If we were to line up a group of people on a football field by height, relatively few people would fall at the extreme tall and short ends. A majority of people would fall in the middle range. When frequency is highest near the mean value (middle) and decreases towards each extreme, it is called a Normal Distribution. The graphed result is a bell shaped curve.

Natural Selection Can Change the Distribution of a Trait Macroevolution is the observable (large) change in the allele frequencies of a population over time. Microevolution occurs on a small scale, within a single population. This can result in one of three paths.

Directional Selection Directional Selection favors phenotypes at one extreme of a trait’s range. Ex: Drug Resistant Bacteria. This phenotype was selected Against when there were no antibiotics. Now that there are antibiotics, this phenotype is now more successful and selected for. Directional selections moves the curve on the graph left or right.

Stabilizing Selection In Stabilizing Selection the intermediate phenotype (median) is favored. Ex: Gall flies and their predators. Woodpeckers feed on larger gall fly larva. Parasitic wasps lay eggs on the smaller gall fly larva. Only the gall fly larva that are medium size have a chance to survive. Stabilizing Selection on a graph looks like Normal Selection.

Disruptive Selection Disruptive Selection occurs when both extreme phenotypes are favored, while individuals with intermediate (middle)phenotypes are selected against by something in nature. Ex: Feather color in male lazuli buntings (a bird). Feathers range from dull brown to bright blue. Dull Brown and Bright blue feather buntings have a better chance of getting a mate than regular blue birds do. The brown males are successful because the aggressive bright blue males do not see them as a threat. The regular blue birds are frequently attacked because they are seen as a threat. The graph in disruptive selection has two curves, one at each extreme.

Other Mechanisms of Evolution Words to Know: Gene Flow, Genetic Drift, Bottleneck Effect, Founder Effect, Sexual Selection, homozygous, heterozygous.

Gene Flow When an organism joins a new population and reproduces, its alleles become part of that population’s gene pool. At the same time its genes are removed from its previous population. The movement of alleles from one population to another is called Gene Flow. Gene flow increases genetic variation. A lack of gene flow can cause speciation.

Genetic Drift Genetic Drift is the change in allele frequencies due to chance. Two processes commonly cause populations to become small enough for genetic drift to occur.

Bottleneck Effect The Bottleneck Effect is genetic drift that occurs after an event greatly reduces the size of a population. Ex: Overhunting of northern elephant seals during the 1800’s. The population got reduced to about 20 seals that did not represent the genetic diversity of the original population.

Founder Effect The Founder Effect is genetic drift that occurs after a small number of individuals colonize a new area. The gene pools of these new populations are often very different from those of the larger population. Ex: The Amish of Lancaster Pennsylvania have a high rate of a rare form of Dwarfism. Because they are such a small community, this trait is common in the population.

Effects of Genetic Drift The population loses genetic variation. Less likely to have individuals to adapt. Alleles that are lethal can become more common.

Sexual Selection Mating has an important effect on the evolution of a population. Sexual Selection occurs when certain traits increase mating success. There are two types of sexual selection: 1. Intrasexual Selection involves competition among males. Whoever wins get the girl. 2. Intersexual Selection occurs when males display certain traits that attract the females, such as peacock feathers.

Review Questions 1. Draw the three types of selection curves: 2. What is a mutation? 3. What is a gene pool? 4. What is speciation?

Review Questions 1. Draw the three types of selection curves:

Review Questions Cont. What is a mutation? A mutation is a random change in the DNA of a gene What is a gene pool? All the possible genes available in a population. What is speciation? The formation of a new species.

Hardy-Weinberg Equilibrium Words to Know: Hardy-Weinberg Equilibrium, equilibrium, dominant, recessive, homozygous, heterozygous.

Hardy-Weinberg Equilibrium Hardy and Weinberg showed that genotype frequencies in a population will stay the same over time as long as 5 conditions are met: 1. Must be a very Large Population (NO genetic drift). 2. No emigration or immigration (NO gene flow). 3. No mutations (NO new alleles). 4. Must have Random Mating (NO sexual selection allowed). 5. No Natural Selection (all traits must equally aid in survival). Real populations rarely meet all five requirements

The Hardy-Weinberg Equation For traits in a simple dominant-recessive systems, biologists can predict genotype frequencies using the Hardy-Weinberg equation. P2 + 2pq + q2 = 1  p = frequency of the dominant allele  q = frequency of the recessive allele. In Hardy-Weinberg Equilibrium, the equation ALWAYS equals 1. If the equation DOES NOT equal 1, evolution is occurring.

Hardy Weinberg Equation

There are Five Factors that can Lead to Evolution 1. Genetic Drift – allele frequency can change due to chance alone. 2. Gene Flow – the movement of alleles from one place to another change the allele frequencies of the population. 3. Mutation – new alleles can form through mutations, and these create the genetic variation needed for evolution. 4. Sexual Selection – certain traits may improve mating success which cause an increase in that allele frequency. 5. Natural Selection – Certain traits may be an advantage for survival so alleles for these traits increase in frequency.

Speciation Through Isolation Words to Know: Reproductive Isolation, Speciation, Behavioral Isolation, Geographic Isolation, Temporal Isolation.

Isolation of Populations If gene flow between two populations stops for any reason, the population are said to be isolated. As they adapt to their new environments, their gene pools may change. Reproductive Isolation occurs when members of different populations can no longer mate successfully with one another. Speciation is the rise of two or more species from on existing species.

Behavioral Barriers Behavioral Isolation is isolation caused by differences in courtship or mating behaviors. Ex: Fireflies. Male and female fireflies produce patterns of light flashes that attract only their own species.

Geographic Barriers Geographic Isolation involves physical barriers that divide a population into two or more groups. These can be rivers, mountains, and dried lakebeds. Ex: The isthmus of Panama separated many aquatic species that then evolved separately.

Temporal Barriers Temporal Isolation exists when timing prevents reproduction between populations. Some members of a population may show signs of courtship at different times. Ex: flowers bloom at different times of year.

Patterns in Evolution Words to Know: Convergent Evolution, Divergent Evolution, Coevolution, Extinction, Punctuated Equilibrium, Adaptive Radiation

Evolution through Natural Selection is NOT Random. Individuals with traits that are better adapted for their environment have a better chance of surviving and reproducing than do individuals without these traits. Natural selection always pushes traits in an advantageous direction. The environment controls the direction taken by natural selection.

1. Convergent Evolution Different species often must adapt to similar environments. Evolution toward similar characteristics in unrelated species is called Convergent Evolution. Ex: Shark and Dolphins are not related yet they have evolved similar tail fins.

2. Divergent Evolution When closely related species evolve in different directions, they become increasing different in Divergent Evolution. Ex: Red Fox and Kit fox: though closely related they have developed different characteristics based on the environment they live in.

3. Coevolution Coevolution is the process in which two or more species evolve in response to changes in each other. Ex: Bees and flowers.

Evolutionary Arms Race Coevolution can also occur in competitive relationships. Ex: Many plants produce defense chemicals to discourage herbivores from eating them. Natural selection then favors the herbivores who can overcome the effect of the toxins. Ex: Thick shells and spines of murex snails are an adaptive response to predation by crabs. In turn, crabs have evolved strong claws.

Species Can become Extinct The elimination of a species from Earth is Extinction. There are two types of extinctions involved in evolution: 1. Background extinctions – occur continuously at a slow rate. (usually effect one or few species in a small space). 2. Mass Extinctions – many species are destroyed suddenly. (ice age, meteors).

Speciation Often Occurs in Patterns There are repeating patterns in the history of life. The Theory of Punctuated Equilibrium states that episodes of speciation occur suddenly in geologic time and are followed by long periods of little evolutionary change. This opposed Darwin’s theory of gradualism (slow, steady evolution). Adaptive Radiation the diversification of one ancestral species into many descendant species. Ex: Following the mass extinction at the end of the Cretaceous Period 65 million years ago, Adaptive radiation of mammals occurred.