Chapter 22 & 23

Assuming that a population is in Hardy-Weinberg equilibrium, write the equation that describes genotypic frequencies.

(p^2)+2pq+(q^2)=1 is the equation that describes the genotypic frequencies in a population that is in Hardy-Weinberg equilibrium. Z.L.

What 3 conditions must be met in order for natural selection to occur and result in evolutionary change?

-Variation in traits -Traits are inherited -Differential success in reproduction

How can a change in a population's food source result in evolution by natural selection? Provide evidence.

A change in a population's food source can result in evolution by natural selection because it favors organisms with certain traits, making those organisms more capable of obtaining food therefore surviving and reproducing. The organism without these traits are less fit for the environment, which will eventually lead to the diminished population of those without the trait and the increase of those which are able to obtain the food. One example is the height of giraffes. If the tall giraffes can reach the leaves of tall trees and shorter giraffes cannot, the shorter will die off and the taller will continue to survive and reproduce, passing tall genes on to subsequent generations.

In reference to the Hardy-Weinberg Principle, define the following: p2, 2pq, & q2

According to the Hardy-Weinberg Principle, p^2 refers to the expected frequency of the homozygous dominant genotype, 2pq refers to the expected frequency of the heterozygous genotype, and q^2 refers to the expected frequency of the homozygous recessive genotype.

Define adaptive evolution. How is this a passive process?

Adaptive evolution is any evolution that results in a better match between an organism and its environment. Adaptive evolution is a result of mutations that happen to be beneficial and are selected by the environment. Organisms do not exert an effort to mutate, meaning this is a passive process.

What is gene flow? Provide an example to illustrate the concept.

Allele frequencies can also change by gene flow, the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes. For example, suppose that near our original hypothetical wildflower population there is another population consisting primarily of white-flowered individuals. Insects carrying pollen from these plants may fly to and pollinate plants in our original population. The introduced alleles would modify our original population's allele frequencies in the next generation. Because alleles are exchanged between populations, gene flow tends to reduce the genetic differences between populations. In fact, if it is extensive enough, gene flow can result in two populations combining into a single population with a common gene pool.

Describe how the marsupial-placental convergence supports the principle of evolution by natural selection.

Although marsupials have evolved independently from different ancestors, they have adapted to similar environments in similar ways. The desired trait of the marsupials was selected upon in different areas, resulting in the trait evolving by convergent evolution. Example: The ability to glide through the air evolved independently in the sugar glider in Australia, a marsupia,l and the flying squirrel in North America, a placental or eutherian (the ability to glide in the two organisms serves the same function, but evolved independently).

Besides anatomical homologous structures, list and briefly explain 3 other types of evidence from homology that supports the principle of evolution by natural selection.

Anatomical structures, structures in different species with common purposes, but not common ancestry, Vestigal structures, DNA and RNA, the genetic code.

How does artificial selection provide support for the principle of evolution by natural selection?

Artificial selection allowed Darwin some observations that supported his theory of evolution such as the fact that members of a population vary in their inherited traits. As humans select for certain characteristics in offspring - example wolves, these characteristics become more abundant in subsequent generations. The accumulation of these traits result in the wide diversity we see in dogs today.

Explain the term "convergent evolution".

Convergent evolution is the independent evolution of similar features in different lineages. In such examples in which species share features because of convergent evolution, the resemblance is said to be analogous, not homologous. Analogous features share similar function, but not common ancestry, while homologous features share common ancestry, but not necessarily similar function. N.K. An example of convergent evolution would be flight in insects and bats.

Describe the two observations from which Darwin drew the two inferences that explain natural selection. Go ahead and summarize the two inferences as well, so you have them in your notes.

Darwin observed that traits vary in a population and that more offspring are produced than can survive. This allowed Darwin to infer that individuals with traits that allow them to survive more easily will leave more offspring. Darwin inferred that favorable traits will accumulate in a population as unfit members die off.

Evolution was not an idea original to Darwin, so what was Darwin's key contribution to this theory?

Darwin's key contribution to the theory of evolution was natural selection. Natural selection states that individuals that have certain inherited traits tend to survive at higher rates than other individuals because of those traits. Although Lyell published the idea of evolution first, Darwin proposed the mechanism of natural selection that explains how evolution occurs.

Define "descent with modification"

Descent with modification summarizes Charles Darwin's view of life. It proposes the idea that all organisms share a distant ancestor and as a population, their traits are selected by their environment so that the population evolves. This process of modification is a passive process in which the environment works on an organism.

Distinguish between the three types of selection (disruptive, stabilizing, directional). You can use an illustration if you think that would be helpful

Directional- shifts the overall makeup of the population by favoring variants that are at one extreme of the distribution. Common when a population's environment changes or when members migrate Disruptive- favors variants at both ends of the distribution-- intermediate types are selected against Stabilizing- removes extreme variants from the population and preserves intermediate types (other sides of the intermediate are selected against) Never results in a new species.

Define "fitness" (as it is used in evolutionary biology)

Fitness is defined as an individual's ability to contribute to the gene pool of the following generation, relative to the contribution of other individuals, based on their possession of certain traits.

Summarize the different lines of evidence supporting the hypothesis that cetaceans descended from land mammals and are closely related to even-toed ungulates.

Fossil evidence has shown that cetaceans have many structural similarities with even-toed ungulates, proving that the two shared a common ancestor and developed differently due to descent with modification. Scientists also discovered new fossils that document cetacean's loss of hind legs and growth of flippers and fluke tails, giving further evidence that they originated from land mammals. C.A. DNA evidence can also provide evidence of relation.

Describe how fossils change as you dig deeper through the sedimentary layers of rock.

Fossils change as you dig deeper through the sedimentary layers of rock. The fossils of new species appear in all of the different strata, or levels. The older, or further down the strata, the more dissimilar the species are to life today and they are more likely to be extinct. As you move up the strata, new organisms can be found and they become increasingly similar to the species alive today.

Why are organisms not perfect?

Four Reasons: Selection can act only on existing variations: natural selection only favors fittest phenotypes (may not be the ideal traits); new advantageous alleles do no arise on demand Evolution is limited by historical constraints: evolution doesn't scrap ancestral anatomy and build new complex structure from scratch-- co-opts and adapts them to new situations Adaptations are often compromises: each organism must do many different things Chance, natural selection, and the environment interact: chance events can affect the subsequent evolutionary history of populations *Natural Selection operates on a "better than" basis

Summarize the four effects of genetic drift.

Genetic drift can have severe effects on the allele frequencies of smaller communities. Their gene pools are much smaller, and would be affected on a much greater scale if an allele were to leave or enter the population. Allele frequencies may also change randomly because of alleles going in and out of the community, which could potentially harm the population because the traits are no longer in accordance with the environment. If there is enough allele movement out of a population, the allele may be lost from the population forever, changing how population adapts to the environment if any major changes occur. Finally, genetic drift may fix certain alleles in the community that have no effect on the organisms, making them harmful to the population.

Why is genetic variation a prerequisite for evolution?

Genetic variation results in some individuals having a better match to the environment thus having a higher chance to survive and reproduce.

Explain "heterozygote advantage" and describe an example.

Heterozygote advantage is exhibited when individuals who are heterozygous for a particular gene have better fitness than both kinds of homozygotes. For example, heterozygotes for sickle-cell allele are the most fit because they are protected from the most severe effects of malaria because the sickled red blood cells are destroyed rapidly but the parasites inside normal red blood cells are preserved. On the other hand, those recessive for this gene cannot preclude the damage of sickle-cell disease from occurring and are affected. This tends maintain the deleterious, recessive allele in the population.

Explain what is meant by homologous structures and describe how they serve as support for the principle of evolution by natural selection.

Homologous structures are structures in different species that are similar because of common ancestry. Homologous structures serve as support for the principle of evolution by natural selection because it supports the idea that species evolve from another species, so they have common structures.

Distinguish between Lamarck's concept of evolution and Darwin's.

Lamarck's concept of evolution was based on the idea that evolution occurred because organisms have a drive to be more complex. His idea was the use and disuse principle where he believed that populations develop traits because they use them more. Darwin's concept of evolution was centered around the idea that evolution occurs due to adaption to the environment and natural selection. Adaption is an inherited trait that enhances the survival of an organism in a specific environment not a trait that is developed by one individual.

How does the emergence of drug-resistant bacteria provide evidence of evolution?

Mutation is the raw material for evolution. In a population of bacteria, mutations occur randomly. A certain mutation could confer drug-resistance. If this mutation occurs in bacteria cell, that cell would have a better chance at surviving and reproducing, passing that gene on to subsequent generations. Bacteria without the gene will die. In this manner, a population of bacteria evolves.

What is the primary mechanism that is responsible for evolutionary change?

NATURAL SELECTION

Define natural selection. From your definition, identify the three conditions that must be met in order for natural selection to occur and result in evolutionary change.

Natural selection is a process in which individuals that have inherited traits tend to survive and reproduce at a higher rate than other individuals because of those traits. Natural selection is a passive process that works on the traits or DNA that already exist in a population. The three conditions that must be met in order for natural selection to occur and result in evolutionary change are traits, inherited, and selection pressure.

What was the driving force behind the evolution of the 14 species of finches on the Galapagos?

Natural selection, Food source.

What are three mechanisms responsible for evolutionary change? Which is the primary agent of change?

Natural selection, genetic drift, and gene flow are responsible for evolutionary change. Natural selection is the predominant mechanism causing evolution.

List the 5 conditions that must be met by a population for genotypes to remain unchanged from generation to generation (ie., a population in Hardy-Weinberg equilibrium)

No mutations can be present because they can alter allele frequencies by deleting or duplicating genes. Random mating must occur because if individuals mate among one subset of the populations, there is no random exchange of gametes and genotype frequencies can change. Natural selection cannot be present because it favors individuals possessing certain genotypes, causing not only their survival but reproduction and altering allele frequencies of the offspring generation. A large population must be present to reduce chance events that may alter allele frequencies (genetic drift cannot be facilitated as easily among so many individuals). Finally no gene flow can occur because moving alleles into or out of the population, can change allele frequencies.

List and briefly explain the 5 agents of evolutionary change.

One agent of evolutionary change is that there must be mutations. The gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated. Another agent of evolutionary change is that there must be nonrandom mating. If individuals mate preferentially within a subset of the population, such as their close relatives (inbreeding), random mating of gametes does not occur, and genotype frequencies change. Also, natural selection is an agent of evolutionary change. Differences in the survival and reproductive success of individuals carrying different genotypes can alter allele frequencies. Additionally, small population size is an agent of evolutionary change. The smaller the population, the more likely it is that the allele frequencies will fluctuate by chance from one generation to the next (a process called genetic drift). Lastly, gene flow is an agent of evolutionary change. By moving alleles into or out of populations, gene flow can alter allele frequencies.

List and briefly describe 2 cases in which artificial selection has created substantial changes in a species.

One case in which artificial selection has created substantial changes in a species is in the case of wild mustard. Humans have used artificial selection to create many plants such as kale, brussel sprouts, cabbage, broccoli, and kohlrabi. The wild mustard was bred to produce species carrying desired traits such as leaves, axillary buds, apical buds, flowers, and stems. Another case is the domestication of wolves over time into dogs. Humans have also used artificial selection to breed crops, livestock animals, and other pets with desired traits.

Describe how overreproduction and heritable variation relate to evolution by natural selection.

Over reproduction relates to evolution because as organisms reproduce their traits and characteristics pass down to their offspring. If the organism is unable to reproduce, its traits will not be able to carry on and get passed down to further generations. As an organism continues to reproduce more and more that trait continuously appears in its offspring and then later generations. N.H. Also, Darwin observed that more offspring are born than can survive. This observation lead him to think that certain organisms may be better suited to survive and reproduce, helping form his ideas of natural selection.

How did Darwin's observations of the finches of the Galapagos Islands influence the development of his theory of evolution by natural selection?

See his two observations that led to his two inferences in question below.

What is the value of using the Hardy-Weinberg Principle when researching evolution in a population?

The H-W principle enables us to focus on what causes evolution.

Why was the age of Earth important for Darwin's ideas about evolution?

The age of Earth was important for Darwin's ideas about evolution because for all species to have evolved from one species Earth had to be much older than the age that was currently accepted. Instead of being thousands of years old, the Earth had to be billions of years old for species to have evolved to the point they were at when Darwin developed his idea.

How does genetic drift apply to each of the following? Give an example of each: Founders effect; Bottleneck effect?

The founder effect exhibits the process of genetic drift when a small group of individuals are separated from a larger population due to a chance event and the smaller population develops their own gene pool that is different from that of the original population. For example if a group of individual humans became isolated from their original population due to a storm, they would procreate among themselves, altering allele frequencies and developing a different gene pool from the original population. The bottleneck effect exhibits the genetic drift as the allele frequencies of a population drastically change because of a chance event. For example, if a fire eliminates half of the population, a much smaller group of individuals are left that may over or under represent certain alleles. This lack of genetic variation due to the small population can be detrimental to the surviving individuals.

Identify and describe 4 sources of genetic variation.

The four sources of genetic variation are the formation of new alleles, altering gene number or position, rapid reproduction, and sexual reproduction. The formation of new alleles is caused by mutations, such as point mutations, that make slight changes in the genetic code. Gene number or position can be changed during meiosis, in which genes can be placed in a different place in the chromosome, or other genes can be accidentally duplicated. Even with a slow mutation rate, a rapid reproduction rate can still cause mutations to happen quickly, such as mutations in HIV viruses, which do not repair their genetic material. Sexual reproduction (crossing over and recombination) shuffles existing genes into new genotypes.

What is the raw material of evolution?

The raw material of evolution is genetic variation, which is differences among individuals in the composition of their genes or other DNA segments.

If p is the frequency of allele A, use the Hardy-Weinberg equation to predict the frequency of individuals that have at least one A allele.

p^2+2pq