Module 7 Quiz

Describe how variation can be maintained in a population even though natural selection seems to act against it

A population always shows some genotypic variation. The maintenance of variation is beneficial because populations with limited variation may not be able to adapt to new conditions if the environment changes, and thus may become extinct. How can variation be maintained in spite of selection constantly working to reduce it? First, we must remember that the forces that promote variation are always at work: Mutation still generates new alleles, recombination and independent assortment still shuffle the alleles during gametogenesis, and fertilization still creates new combinations of alleles from those present in the gene pool. Second, gene flow might be occurring between two populations. If the receiving population is small and is mostly homozygous, gene flow can be a significant source of new alleles. Finally, natural selection favors certain phenotypes, but the other phenotypes may remain in the population at a reduced frequency. Disruptive selection even promotes polymorphism (the occurrence of different forms in a population of the same species) in a population. In diploid species, heterozygotes also help maintain variation because they conserve recessive alleles in the population.

1. Describe what the Hardy-Weinberg principle contributes to evolutionary theory. c. genotypic frequencies

It is customary to describe the gene pool of a population in terms of genotype and allele frequencies. The genotype frequency is the percentage of a specific genotype—for example, homozygous dominant individuals—in a population.

Explain what is required (three things) for natural selection to occur

Evolution by natural selection involves: 1. Variation. The members of a population differ from one another. 2. Inheritance. Many of these differences are heritable genetic differences. 3. Increased fitness. Individuals that are better adapted to their environment are more likely to reproduce, and their fertile offspring will make up a greater proportion of the next generation.

Explain the relationship between a frequency and a percentage

Frequency is often written as a decimal, and a percentage is written as a percent. Frequency is the number of occurrences of a periodic or recurrent process per unit time. Allele frequency is the number of individual alleles of a certain type, divided by the total number of alleles of all types in a population. · Genotype and allele frequencies are represented by a percentage o The genotype frequency is the percentage of a specific genotype—for example, homozygous dominant individuals—in a population. o The allele frequency represents how much a specific allele is represented in the gene pool of the population.

1. Differentiate between the two forms of genetic drift. a. founder effect b. bottleneck effect

Genetic drift is a random process, and therefore it is not likely to produce the same results in different populations. In California, there are a number of cypress groves, each a separate population. The phenotypes within each grove are more similar to one another than they are to the phenotypes in the other groves. Some groves have longitudinally shaped trees, and others have pyramidally shaped trees. The bark is rough in some colonies and smooth in others. The leaves are gray to bright green or bluish green, and the cones are small or large. Because the environmental conditions are similar for all the groves, and no correlation has been found between phenotype and environment across groves, scientists hypothesize that these variations among the populations are due to genetic drift. i. Bottleneck effect- 1. Sometimes a species is subjected to near extinction because of a natural disaster (e.g., earthquake or fire) or because of overharvesting and habitat loss. It is as though most of the population has stayed behind and only a few survivors have passed through the neck of a bottle. Called a bottleneck effect, such an event prevents the majority of genotypes from participating in the production of the next generation. 2. The extreme genetic similarity found in cheetahs is believed to be due to a bottleneck. In a study of 47 different enzymes, each of which can occur in several different forms in other types of cats, all the cheetahs studied had exactly the same form. This demonstrates that genetic drift can cause certain alleles to be lost from a population. Exactly what caused the cheetah bottleneck is not known. Several hypotheses have been proposed, including that cheetahs were slaughtered by nineteenth-century cattle farmers protecting their herds, were captured by Egyptians as pets 4,000 years ago, or were decimated by a mass extinction event tens of thousands of years ago. Today, cheetahs suffer from relative infertility because of the intense inbreeding that occurred after the bottleneck. ii. Founder Effect- 1. The founder effect is a mechanism of genetic drift in which rare alleles, or combinations of alleles, occur at a higher frequency in a population isolated from the general population. After all, founding individuals contain only a fraction of the total genetic diversity of the original gene pool. The alleles carried by their founder or founders are dictated by chance alone. The Amish of Lancaster Counter, Pennsylvania, are an isolated group founded by German settlers. Today, as many as 1 in 14 individuals in this population carry a recessive allele that causes an unusual form of dwarfism (affecting only the lower arms and legs) and polydactylism (extra fingers). In most populations, only 1 in 1,000 individuals has this allele.

1. Describe what the Hardy-Weinberg principle contributes to evolutionary theory. b. allele frequencies

If there are two people in a population and one is Bb and the other one is bb, you have a total of four alleles (B, b, b, b). B= brown (dominant) b= blue (recessive) the frequency of the brown allele is f(B)= 1/4 or .25 or 25% The frequency of the blue allele is f(b) = 3/4 or .75 or 75% 1/4 + 3/4 = 1 or 100% 25% + 75% = 100% Lowercase p is the frequency of the dominant allele Lowercase q is the frequency of the recessive allele p + q = 1 or 100% We assumed there is only two alleles in this population for this trait, so the frequency of the dominant ones plus the frequency of the recessive ones, since everyone is going to have one of those two, if you add those two frequencies together, it will add up to 100% i. An allele is a variant of a gene. You get a variant of a gene from your mother, and you get another variant of the gene from the father. When we are talking about the allele, we are talking about that specific variant that you got from your mother or your father. i. It is customary to describe the gene pool of a population in terms of genotype and allele frequencies. The allele frequency represents how much a specific allele is represented in the gene pool of the population.

Evaluate the validity of this quote: "Individuals evolve; not populations."

Many traits can change temporarily in response to a varying environment. For example, the color change in the fur of an Arctic fox from brown to white in winter, the increased thickness of your dog's fur in cold weather, or the bronzing of your skin when exposed to the sun lasts only for a season. These are not evolutionary changes. Changes to traits over an individual's lifetime are not evidence than an individual has evolved, because these traits are not heritable. In order for traits to evolve, they must have the ability to be passed on to subsequent generations. Evolution causes change in a heritable trait within a population, not within an individual, over many generations. Darwin observed that populations, not individuals, evolve, but he could not explain how traits change over time. Now we know that genes interact with the environment to determine traits. Because genes and traits are linked, evolution is really about genetic change—or more specifically, evolution is the change in allele frequencies in a population over time. This type of evolution is called microevolution. Connections: Scientific Inquiry. Why don't individuals evolve? Evolution results in genetic change in a population over periods of time. While individual organisms, such as humans, may develop new skills and abilities (such as learning a new language or playing a guitar), their genetic material remains unchanged. These new abilities are not passed on to the next generation and do not change the genetic composition of the population.

1. Explain how microevolution occurs when allele frequencies change from one generation to the next.

Microevolution is the change in allele frequencies in a population over time. Sexual reproduction alone cannot bring about a change in genotype and allele frequencies. Also, the dominant allele need not increase from one generation to the next. Dominance does not cause an allele to become a common allele. The conditions of Hardy-Weinberg are rarely, if ever, met, and genotype and allele frequencies in the gene pool of a population do change from one generation to the next. Therefore, microevolution does occur, and the extent of change can be measured. Microevolution can be detected and measured by noting the amounts of deviation from a Hardy-Weinberg equilibrium of genotype frequencies in the gene pool of a population. An example of microevolution: For genotype frequencies to be subject to natural selection, they must result in a change of phenotype frequencies. Industrial melanism, an increase in the frequency of a dark phenotype due to pollution, provides us with an example. We supposed that only 36% of our moth population was dark-colored d(homozygous dominant plus heterozygous). Why might that be? Before the rise of the industry, dark-colored moths rested on light tree trunks, where they were seen and eaten by birds. However, with industrial development, the trunks of trees darkened as a result of air pollution, and the light-colored moths became visible and were eaten more often. Predatory birds acted as a selective agent, and microevolution occurred—in the mid 1950s, the number of dark-colored moths in some Great Britain populations exceeded 80%. Aside from showing that natural selection can occur within a short period of time, our example illustrates that a change in gene pool frequencies does take place as microevolution occurs. Causes of microevolution: · Natural selection · Genetic mutation · Gene flow · Nonrandom mating · Genetic Drift o Bottleneck effect o Founder effect

Explain why adaptations are not always perfect

Natural selection doesn't always produce organisms that are perfectly adapted to their environment. Why not? First, it is important to realize that evolution doesn't start from scratch. Just as you can only bake a cake with the ingredients available to you, evolution is constrained by the available variations. Each species must build upon its own evolutionary history, which limits the amount of variation that may be acted on by natural selection. Second, as adaptations are evolving in a species, the environment may also be changing. Most adaptations provide a benefit to the species for a specific environment for a specific time. As the environment changes, the benefit of a certain adaptation may be minimized. It is also important to recognize that imperfections are common because of necessary compromises. The success of humans is attributable to their dexterous hands, but the spine is subject to injury because the vertebrate spine did not originally evolve to stand erect. A feature that evolves has a benefit that is worth the cost. For example, the benefit of freeing the hands must have been worth the increased cost of spinal injuries from assuming an erect posture.

Explain how heterozygotes maintain variation

Only alleles that are expressed (cause a phenotype difference) are subject to natural selection. In diploid organisms, this fact makes the heterozygote a potential protector of recessive alleles that might otherwise be weeded out of the gene pool. Because the heterozygote remains in a population, so does the possibility of the recessive phenotype, which might have greater fitness in a changed environment. When, over time, environmental conditions cause natural selection to maintain two different alleles of a gene at a certain ratio, the situation is called balanced polymorphism. Sickle-cell disease offers an example of a balanced polymorphism.

Explain the purpose of the Hardy - Weinberg Model of Genetic Equilibrium

These conditions are rarely, if ever, met, and genotype and allele frequencies in the gene pool of a population do change from one generation to the next. Therefore, microevolution does occur, and the extent of change can be measured. The significance of the Hardy-Weinberg principle is that it tells us what factors cause evolution—those that violate the conditions listed. Microevolution can be detected and measured by noting the amount of deviation from a Hardy-Weinberg equilibrium of genotype frequencies in the gene pool of a population.

Describe what the Hardy-Weinberg principle contributes to evolutionary theory

The Hardy- Weinberg principle is a useful principle for thinking through what allele frequencies and genotype frequencies might be. This principle can be useful in real life. When people think about a recessive allele that might cause some type of disease, based on the incidence of that disease, people can start to think about what percentage of the population is a carrier (heterozygotes).

1. Describe what the Hardy-Weinberg principle contributes to evolutionary theory. d. Equilibrium

The Hardy-Weinberg equilibrium is a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors. When mating is random in a large population with no disruptive circumstances, the law predicts that both genotype and allele frequencies will remain constant because they are in equilibrium. The Hardy-Weinberg equilibrium can be disturbed by a number of forces, including mutations, natural selection, nonrandom mating, genetic drift, and gene flow. Because all of these disruptive forces commonly occur in nature, the Hardy-Weinberg equilibrium rarely applies in reality. Therefore, the Hardy-Weinberg equilibrium describes an idealized state, and genetic variations in nature can be measured as changes from this equilibrium state.

Describe the five conditions necessary for the H/W model to be valid

The mathematical relationships of the Hardy-Weinberg principle will remain in effect in each succeeding generation of a sexually reproducing population as long as five conditions are met: 1. No mutations: Allelic changes do not occur, or changes in one direction are balanced by changes in the opposite direction. 2. No gene flow: Migration of alleles into or out of the population does not occur. 3. Random mating: Individuals pair by chance, not according to their genotypes or phenotypes. 4. No genetic drift: The population is very large, and changes in allele frequencies due to chance alone are insignificant. 5. Selection: Natural selection is not occurring or does not favor any allele or combination of alleles over another.

polymorphism

The occurrence of different forms in a population of the same species.

1. Describe what the Hardy-Weinberg principle contributes to evolutionary theory. a. p2 + 2pq + q2 = 1.0

We get this equation by squaring both sides of the equation p + q = 1 (p + q)^2 = (1)^2 (p + q)(p + q) = 1 p^2 + pq + pq + q^2 = 1 P2 + 2pq + q2 = 1 · P = the probability of getting one dominant allele (B) · P2 means the probability of getting two dominant alleles, or being homozygous dominant (BB) · Q is the probability of getting one recessive allele · Q2 is the probability of getting two recessive alleles (one from your mother and one from your father), or being homozygous recessive (bb) · 2pq= The probability of being a heterozygote. The probability that from one parent you will inherit the dominant allele and from the other you will inherit the recessive allele. There are two possibilities for to become a heterozygote: you can either get p from mom and q from dad, or q from mom and p from dad. Since there are two possibilities, that is why it is 2pq (pq + pq = 2pq). Lowercase p is the frequency of the dominant allele Lowercase q is the frequency of the recessive allele p + q = 1 or 100% Frequency of dominant allele + frequency of recessive allele = 100% This is because you have a 100% chance of getting either p or q 100% - p = q We assumed there is only two alleles in this population for this trait, so the frequency of the dominant ones plus the frequency of the recessive ones, since everyone is going to have one of those two, if you add those two frequencies together, it will add up to 100% If we know the phenotype of the population, such as knowing that 9% have blue eyes, we can figure out p (frequency of dominant allele) and q (frequency of recessive allele) using the equation p2 + 2pq + q2 = 1. There is a 100% chance that if you were to randomly pick a gene that it is one of these two variants, either p or q. The only way to have blue eyes is if your genotype is homozygous recessive (q2). So 9% have the genotype bb. · Q2 = 9% or 0.09 · Since we know q2, we can find q by taking the square root of 0.09, which is equal to 0.3. · Q = 0.3 · So q = f(b) = 30% , 30% of the genes in the population code for the recessive allele, or the recessive variant. Given this, we can find out p. The rest of the genes must code for p since this is the only other option given that p + q = 100% or 1. · Since q = 30%, p = 70%, or p = f(B) = 70% · P2 = .7 squared à 0.49 or 49% · 2pq = 2(0.7)(0.3) à 0.42 or 42% p2 + 2pq + q2 = 1. P2 = 49% Q2 = 9% 2pq = 42% 42% + 49% + 9% = 100% 49% is homozygous dominant (BB) 9% is homozygous recessive (bb) 42% of the population is going to be heterozygous (Bb)

1. Describe what the Hardy-Weinberg principle contributes to evolutionary theory. e. Five assumptions

a. These assumptions get us a stable allele frequency in the population from generation to generation i. No mutations: Allelic changes do not occur, or change sin one direction are balanced by changes in the opposite direction 1. One of the alleles from generation to generation isn't turning into another one or turning into maybe a different or new type of trait ii. No gene flow: Migration of alleles into or out of the population does not occur iii. Random mating: Individuals pair by chance, not according to their genotypes or phenotypes iv. No genetic drift: The population is very large, and changes in allele frequencies due to chance alone are insignificant 1. Assume large populations v. Selection: Natural selection is not occurring or does not favor any allele or combination of alleles over another 1. It's not like people with one of the alleles or another are going to be more or less likely to reproduce and have viable offspring

1. Differentiate between the three types of natural selection and explain how each can affect a trait in a population (pg 115). a. Directional-

i. Directional selection occurs when an extreme phenotype is favored and the frequency distribution curve shifts in that direction. Such a shift can occur when a population is adapting to a changing environment. i. Resistance to antibiotics and insecticides provides a classic example of directional selection. As you may know, the widespread use of antibiotics and pesticides results in populations of bacteria and insects that are resistant to these chemicals. When an antibiotic is administered, some bacteria may survive because they are genetically resistant to the antibiotic. These are the bacteria that are likely to pass on their genes to the next generation. As a result, the number of resistant bacteria keeps increasing. Drug-resistant strains of bacteria that cause tuberculosis have become a serious threat to the heath of people worldwide. i. Another example of directional selection is the human struggle against malaria, a disease caused by an infection of the liver and the red blood cells. The Anopheles mosquito transmits the disease-causing protozoan Plasmodium from person to person. In the early 1960s, international heath authorities thought malaria would soon be eradicated. A new drug, chloroquine, seemed effective against Plasmodium, and spraying of DDT (an insecticide) had reduced the mosquito population. But by the mid-1960s, Plasmodium was showing signs of chloroquine resistance, and worse yet, mosquitoes were becoming resistant to DDT. A few drug-resistant parasites and a few DDT-resistant mosquitoes had survived and multiplied, shifting the frequency distribution curve toward the resistant type of parasite. i. Another example of directional selection was observed in an experiment performed with guppies. The environment included two areas, one below a waterfall and stocked with pike (a fresh predator of guppies) and the other above the waterfall and lacking pike. Over time, in the lower area, natural selection favored male guppies that were small and drab-colored so that they could avoid detection by the pike. However, when the researchers moved male guppies to the area above the waterfall, the absence of such selection caused a change in the phenotype toward larger, more colorful guppies. i. Figure 15.1 During directional selection, an extreme phenotype is favored, which changes the average phenotype value. i. Figure 15.3 In the presence of selection (predation), the phenotype favored smaller, drab-colored male guppies. However, when the selective force was removed, the phenotype of the male guppies shifted to larger, more colorful individuals.

1. Differentiate between the three types of natural selection and explain how each can affect a trait in a population (pg 115). c. Disruptive

i. In disruptive selection, two or more extreme phenotypes are favored over any intermediate phenotype. Therefore, disruptive selection favors polymorphism, the occurrence of different forms in a population of the same species. For example, British land snails (Cepaea nemoralis) are found in low-vegetation areas (grass fields and hedgerows) and in forests. In low-vegetation areas, thrushes feed mainly on snails with dark shells that lack light bands; in forest areas, they feed mainly on snails with light-banded shells. Therefore, these two distinctly different phenotypes, each adapted to its own environment, are found in this population. i. Figure 15.1 During disruptive selection, two extreme phenotypes are favored, creating two new average phenotype values, one for each phenotype. i. Figure 15.4 Disruptive selection. Disruptive selection favors two extreme phenotypes among snails, no banding and banding. Today, British land snails mainly comprise these two different phenotypes, each adapted to a different habitat.

Describe how gene flow can cause allele frequency changes in a population

o Gene flow, also called gene migration, is the movement of alleles among populations by migration of breeding individuals. Gene flow can increase the variation within a population by introducing novel alleles that were produced by mutation in another population. Continued gene flow due to migration of individuals makes gene pools similar and reduces the possibility of allele frequency differences among populations now and in the future. Indeed, gene flow among populations can prevent speciation from occurring. Due to gene flow, the snake populations in Figure 15.10 are subspecies—different populations within the same species. Despite somewhat distinctive characteristics, there is enough genetic similarity between the populations that these subspecies of Pantherophis obsoleta can readily interbreed when they come into contact with one another.

Describe how genetic drift can cause allele frequency changes in a population

o Genetic drift refers to changes in the allele frequencies of a gene pool due to chance. This mechanism of evolution is called genetic drift because allele frequencies "drift" over time. They can increase or decrease depending on which members of a population die, survive, or reproduce with one another. Although genetic drift occurs in both large and small populations, a larger population is expected to suffer less of a sampling error than a smaller population. Suppose you had a large bag containing 1,000 green balls and 1,000 blue balls, and you randomly drew 10%, or 200, of the balls. Because of the large number of balls of each color in the bag, you can reasonably expect to draw 100 green balls and 100 blue balls, or at least a ratio close to this. It is extremely unlikely that you would draw 200 green or 200 blue balls. But suppose you had a bag containing only 10 green balls and 10 blue balls, and you drew 10%, or only 2 balls. You could easily draw 2 green balls or 2 blue balls, or 1 of each color. o When a population is small, random events may reduce the ability of one genotype with regard to the production of the next generation. Suppose that, in a small population of frogs, certain frogs by chance do not pass on their traits. Certainly, the next generation will have a change in allele frequencies. When genetic drift leads to a loss of one or more alleles, other alleles over time become fixed in the population. § Figure 15.11 Genetic Drift. Genetic drift occurs when a random event changes the frequency of alleles in a population. The allele frequencies of the next generation's gene pool may be markedly different from those of the previous generation. o In an experiment involving brown eye color, each of 107 Drosophila populations was kept in its own culture bottle. Every bottle contained eight heterozygous flies of each sex. There were no homozygous recessive or homozygous dominant flies. For each of the 107 populations of flies, 8 males and 8 females were chosen from the offspring and placed in a new culture bottle. This was repeated for 19 generations. The random selection of males and females acted as a form of genetic drift. By the nineteenth generation, 25% of the populations (culture bottles) contained only homozygous recessive flies, and 25% contained only homozygous dominant flies having the allele for brown eye color. o Genetic drift is a random process, and therefore it is not likely to produce the same results in different populations. In California, there are a number of cypress groves, each a separate population. The phenotypes within each grove are more similar to one another than they are to the phenotypes in the other groves. Some groves have longitudinally shaped trees, and others have pyramidally shaped trees. The bark is rough in some colonies and smooth in others. The leaves are gray to bright green or bluish green, and the cones are small or large. Because the environmental conditions are similar for all the groves, and no correlation has been found between phenotype and environment across groves, scientists hypothesize that these variations among the populations are due to genetic drift. § Bottleneck effect- · Sometimes a species is subjected to near extinction because of a natural disaster (e.g., earthquake or fire) or because of overharvesting and habitat loss. It is as though most of the population has stayed behind and only a few survivors have passed through the neck of a bottle. Called a bottleneck effect, such an event prevents the majority of genotypes from participating in the production of the next generation. · The extreme genetic similarity found in cheetahs is believed to be due to a bottleneck. In a study of 47 different enzymes, each of which can occur in several different forms in other types of cats, all the cheetahs studied had exactly the same form. This demonstrates that genetic drift can cause certain alleles to be lost from a population. Exactly what caused the cheetah bottleneck is not known. Several hypotheses have been proposed, including that cheetahs were slaughtered by nineteenth-century cattle farmers protecting their herds, were captured by Egyptians as pets 4,000 years ago, or were decimated by a mass extinction event tens of thousands of years ago. Today, cheetahs suffer from relative infertility because of the intense inbreeding that occurred after the bottleneck. § Founder Effect- · The founder effect is a mechanism of genetic drift in which rare alleles, or combinations of alleles, occur at a higher frequency in a population isolated from the general population. After all, founding individuals contain only a fraction of the total genetic diversity of the original gene pool. The alleles carried by their founder or founders are dictated by chance alone. The Amish of Lancaster County, Pennsylvania, are an isolated group founded by German settlers. Today, as many as 1 in 14 individuals in this population carry a recessive allele that causes an unusual form of dwarfism (affecting only the lower arms and legs) and polydactylism (extra fingers). In most populations, only 1 in 1,000 individuals has this allele.

1. Differentiate between the three types of natural selection and explain how each can affect a trait in a population (pg 115). b. Stabilizing

i. Stabilizing selection occurs when an intermediate phenotype is favored. With stabilizing selection, extreme phenotypes are selected against, and individuals near the average are favored. This is the most common form of selection because the average individual is well adapted to its environment. i. As an example, consider that when Swiss starlings (Sturnus vulgaris) lay four or five eggs, more young survive than when the female lays more or less than this number. Genes determine physiological characteristics, such as the production of yolk, and behavioral characteristics, such as how long the female will mate, are involved in determining clutch size. i. Figure 15.2 Stabilizing selection. Stabilizing selection occurs when natural selection favors the intermediate phenotype over the extremes. For example, Swiss starlings that lay four or five eggs (usual clutch size) have more young survive than those that lay fewer than four eggs or more than five eggs. [In the image for this figure, the bell curve peak narrows towards the center as time goes by, showing that individuals near the average are favored]. i. Figure 15.1. During stabilizing selection, the intermediate phenotype increases in frequency. i. Connections: Scientific Inquiry. Are there examples of stabilizing selection in humans? Perhaps the best example of stabilizing selection in humans is related to birth weight. Studies in England and the United States in the mid-twentieth century indicated that infants with birth weights between 6 and 8 pounds had a higher rate of survival. Interestingly, advances in medical care for premature babies with low birth weights and the increased use of cesarean sections to deliver high-birth-weight babies have lessened the effects of this stabilizing selection in some parts of the world.

Describe how mutations can cause allele frequency changes in a population

o Mutations, which are permanent genetic changes, are the raw material for evolutionary change. Without mutations, there can be no new variations among members of a population on which natural selection can act. However, the rate of mutations is generally very low—on the order of 1 mutation per 100,000 cell divisions. In addition, many mutations are neutral, meaning that they are not selected for or against by natural selection. Prokaryotes do not reproduce sexually and therefore are more dependent than eukaryotes on mutations to introduce variations. All mutations that occur and result in phenotypic differences can be tested by the environment. However, in sexually reproducing organisms, mutations, if recessive, do not immediately affect the phenotype. o In a changing environment, even a seemingly harmful mutation that results in a phenotypic difference can be the source of an adaptive variation. For example, the water flea Daphnia ordinarily thrives at temperatures around 20 C but there is a mutation that requires Daphnia to live at temperatures between 25 C and 30 C. The adaptive value of this mutation is entirely dependent on environmental conditions.

Describe how nonrandom mating can cause allele frequency changes in a population

o Random mating occurs when individuals select mates and pair by chance, not according to their genotypes or phenotypes. Inbreeding, or mating between relatives, is an example of nonrandom mating. Inbreeding does not change allele frequencies, but it does gradually increase the proportion of homozygotes, because the homozygotes that result must produce only homozygotes. o Assortative mating occurs when individuals tend to mate with those that have the same phenotype with respect to a certain characteristic. In humans, cultural differences often cause individuals to select members of their own group. Assortative mating causes the population to subdivide into two phenotypic classes, between which gene exchange is reduced. Homozygotes for the gene loci that control the trait in question increase in frequency, and heterozygotes for these loci decrease in frequency. o Sexual selection favors characteristics that increase the likelihood of obtaining mates, and in this way it promotes nonrandom mating. In most species, males that compete best for access to females and/or have a phenotype that attracts females are more apt to mate and have increased fitness.

Differentiate between population, population genetics, and gene pool

· Population- A group of individuals of a species that can interbreed. The number of organisms of the same species that live in a particular geographic area at the same time, with the capability of interbreeding. A population is defined as a group of individuals of the same species living and interbreeding within a given area. o Evolution causes change in a heritable trait within a population, not within an individual, over many generations · Population genetics- The study of how populations of a species change genetically over time, leading to a species evolving. A field of biology that studies the genetic composition of biological populations, and the changes in genetic composition that result from the operation of various factors, including natural selection. Involves the study of factors that cause changes in allele frequency like natural selection, genetic mutation, gene flow, nonrandom mating, and genetic drift (allele frequency means how often certain alleles turn up within a population), and those changes are at the heart of how and why evolution happens. o In population genetics, the various alleles at all the gene loci in all individuals make up the gene pool of the population. · Gene pool- The collection of different genes within an interbreeding population. The various alleles at all the gene loci in all individuals make up the gene pool of the population. It is customary to describe the gene pool of a population in terms of genotype and allele frequencies. The genotype frequency is the percentage of a specific genotype—for example, homozygous dominant individuals—in a population. The allele frequency represents how much a specific allele is represented in the gene pool of the population.

1. Describe what the Hardy-Weinberg principle contributes to evolutionary theory. phenotype frequency

·Let's say we have a population with two people. One is Bb and the other one is bb. B= brown b= blue Allele frequency is different from phenotype frequency. The percent of brown-eyed people, given that there is two people in the population where only one of the people is exhibiting the phenotype of brown eyes, the % of brown eyed people = ½. · Similarly, the percentage of people who are blue-eyed is also ½ because one of the two people is exhibiting blue eyes.