Multiple Choice Questions on Acclimation, Adaptation, Fitness, Evolution, and Theory PDF

Multiple-Choice Questions on Acclimation, Adaptation, Fitness, Evolution, and Theory 1. Which of the following best describes acclimation? ○ A) A heritable change in phenotype in response to environmental pressures. ○ B) A genetic change in a population over generations....

Multiple-Choice Questions on Acclimation, Adaptation, Fitness, Evolution, and Theory 1. Which of the following best describes acclimation? ○ A) A heritable change in phenotype in response to environmental pressures. ○ B) A genetic change in a population over generations. ○ C) A change in an individual’s phenotype in response to environmental conditions, but it is not heritable. ○ D) The process by which populations evolve over time. 2. What is the key difference between acclimation and adaptation? ○ A) Acclimation occurs in populations, while adaptation occurs in individuals. ○ B) Acclimation is not heritable and does not occur at the population level, whereas adaptation is heritable and occurs at the population level. ○ C) Acclimation is driven by natural selection, while adaptation is not. ○ D) Acclimation is always beneficial, whereas adaptation is never beneficial. 3. How is fitness defined in the context of evolution? ○ A) The physical size and strength of an organism. ○ B) The ability of an organism to survive and reproduce in its environment compared to others. ○ C) The number of offspring an individual can produce in its lifetime. ○ D) The total number of alleles in a population. 4. What does evolution refer to? ○ A) The process by which individuals adapt to their environment during their lifetime. ○ B) A change in allele frequency in a population over generations. ○ C) The sudden appearance of new traits in a species. ○ D) The development of new species from a single organism. 5. What is a "theory" in scientific terms? ○ A) A hypothesis that is yet to be tested. ○ B) A thoroughly tested and confirmed explanation for observations or phenomena. ○ C) A guess about how things work in nature. ○ D) A law that describes how the world works. Answer Key: 1. C) A change in an individual’s phenotype in response to environmental conditions, but it is not heritable. 2. B) Acclimation is not heritable and does not occur at the population level, whereas adaptation is heritable and occurs at the population level. 3. B) The ability of an organism to survive and reproduce in its environment compared to others. 4. B) A change in allele frequency in a population over generations. 5. B) A thoroughly tested and confirmed explanation for observations or phenomena. Multiple-Choice Questions on Evolutionary Evidence 1. What are transitional features in the fossil record? ○ A) Traits that appear suddenly in a species. ○ B) Intermediate states between ancestral and descendent forms of a trait. ○ C) Features that are no longer present in modern organisms. ○ D) Traits that appear in every generation of a species. 2. What does biogeography study? ○ A) The physical appearance of organisms. ○ B) The geographical distribution of species and how it relates to Earth's geologic history. ○ C) The behavior of animals in different environments. ○ D) The genetic mutations within a population. 3. What is a key observation made by biogeographers about species distributions? ○ A) Similar species are found in different parts of the world. ○ B) Modern species tend to resemble fossils from the same geographic area. ○ C) Species from the same region are always genetically identical. ○ D) Fossils do not match the species living in the same geographic regions. 4. What are vestigial structures? ○ A) Features that serve a current function in an organism. ○ B) Structures that are fully functional in all organisms. ○ C) Anatomical features that have no or reduced function compared to their ancestral form. ○ D) Structures that evolve rapidly and change function over time. 5. What do homologies provide evidence of? ○ A) The same function of a trait in different organisms. ○ B) The genetic similarity between unrelated species.  ○ C) Are features that share a similar structure or pattern due to being inherited from a common ancestor;Evolutionary relationships between species, indicating a common ancestor. ○ D) The way species develop independently from one another. Answer Key: 1. B) Intermediate states between ancestral and descendent forms of a trait. 2. B) The geographical distribution of species and how it relates to Earth's geologic history. 3. B) Modern species tend to resemble fossils from the same geographic area. 4. C) Anatomical features that have no or reduced function compared to their ancestral form. 5. C) Evolutionary relationships between species, indicating a common ancestor. One common misconception is that evolution is "just a theory” Certainly! Here's a multiple-choice exam based on the information you provided about Jean-Baptiste Lamarck, Charles Darwin, and Alfred Russell Wallace: Multiple-Choice Exam: Evolutionary Theory 1. What mechanism of evolution did Jean-Baptiste Lamarck propose in 1809? ○ A) Natural selection ○ B) Inheritance of acquired characteristics ○ C) Genetic mutation ○ D) Punctuated equilibrium 2. Why was Lamarck's theory of inheritance of acquired characteristics criticized? ○ A) It was too focused on genetic mutations. ○ B) It lacked sufficient evidence to support the idea that acquired traits could be passed down to offspring. ○ C) It ignored environmental factors. ○ D) It was based on religious principles rather than scientific evidence. 3. What theory did Charles Darwin propose in 1858? ○ A) The theory of inheritance of acquired characteristics ○ B) The theory of evolution by natural selection ○ C) The theory of genetic drift ○ D) The theory of punctuated equilibrium 4. How long did Charles Darwin spend gathering evidence before publishing his theory of natural selection? ○ A) 5 years ○ B) 10 years ○ C) 20 years ○ D) 50 years 5. In what year did Charles Darwin publish his famous book, On the Origin of Species? ○ A) 1809 ○ B) 1858 ○ C) 1859 ○ D) 1865 6. Who independently conceived the mechanism of natural selection around the same time as Charles Darwin? ○ A) Jean-Baptiste Lamarck ○ B) Alfred Russell Wallace ○ C) Gregor Mendel ○ D) Thomas Malthus 7. What significant event happened in 1858 regarding Darwin and Wallace's theories? ○ A) Lamarck published his theory of inheritance of acquired characteristics. ○ B) Darwin and Wallace presented their papers on natural selection jointly at the Linnean Society. ○ C) Darwin published On the Origin of Species. ○ D) Wallace introduced the concept of genetic mutation. 8. What was the key difference between Lamarck's and Darwin's theories of evolution? ○ A) Lamarck believed in gradual, small changes, while Darwin believed in rapid changes.  ○ B) Lamarck focused on inheritance of acquired traits, while Darwin emphasized natural selection. ○ C) Lamarck's theory was based on the idea of a divine creator, while Darwin’s was based on scientific evidence. ○ D) Lamarck believed in common ancestry, while Darwin did not. 9. Which of the following is NOT a concept associated with Darwin’s theory of evolution by natural selection? ○ A) Variation in traits exists within populations. ○ B) Organisms change through inheritance of acquired characteristics. ○ C) Differential reproduction occurs based on survival and fitness. ○ D) Beneficial traits become more common in future generations. 10. What role did Alfred Russell Wallace play in the development of evolutionary theory? ○ A) He rejected the concept of natural selection. ○ B) He independently developed the idea of natural selection, prompting Darwin to publish his work. ○ C) He was the first to propose the inheritance of acquired traits. ○ D) He supported Lamarck’s theory of evolution. Answer Key: 1. B) Inheritance of acquired characteristics 2. B) It lacked sufficient evidence to support the idea that acquired traits could be passed down to offspring. 3. B) The theory of evolution by natural selection 4. C) 20 years 5. C) 1859 6. B) Alfred Russell Wallace 7. B) Darwin and Wallace presented their papers on natural selection jointly at the Linnean Society. 8. B) Lamarck focused on inheritance of acquired traits, while Darwin emphasized natural selection. 9. B) Organisms change through inheritance of acquired characteristics. 10. B) He independently developed the idea of natural selection, prompting Darwin to publish his work. Based on the information you've provided, here is a multiple-choice exam about the concepts of natural selection and evolutionary theory: Multiple-Choice Exam: Natural Selection and Evolutionary Change 1. What does heritable variation in traits within a population mean? ○ A) Individuals in a population look identical and do not differ. ○ B) Traits are passed from one generation to the next through genetic inheritance, and individuals differ based on these traits. ○ C) Individuals do not inherit traits; they only acquire them during their lifetime. ○ D) All individuals have the same traits, and there is no variation. 2. Which of the following is an example of differential reproduction in a population? ○ A) All individuals in a population survive equally well and reproduce at the same rate. ○ B) Some individuals survive and reproduce more successfully because of certain traits, such as better camouflage or faster speed. ○ C) Individuals in a population have no traits that affect their survival or reproduction. ○ D) All individuals in a population experience the same rate of survival but differ in how they attract mates. 3. What is meant by "fitness" in the context of natural selection? ○ A) The ability of an individual to survive but not reproduce. ○ B) The ability of an individual to produce more offspring compared to other individuals in the population. ○ C) The physical strength of an individual. ○ D) The appearance of an individual in relation to others in the population. 4. How does natural selection lead to changes in a population over generations? ○ A) By increasing the genetic diversity of the population. ○ B) By ensuring that all individuals in the population have equal reproductive success. ○ C) By favoring individuals with advantageous traits, leading to an increase in those traits in future generations.  ○ D) By eliminating all traits that are not beneficial to survival. 5. Which of the following is a consequence of differential reproduction? ○ A) All individuals in a population will eventually have the same genetic makeup. ○ B) Traits that improve reproductive success become more common in the population over time. ○ C) Individuals do not reproduce, and no offspring are produced. ○ D) The population becomes extinct due to lack of variation. 6. What is the main driving force behind evolutionary change in a population according to natural selection? ○ A) Random changes in genetic material. ○ B) Differential reproduction based on inherited traits that affect survival and reproduction. ○ C) Inheritance of acquired traits. ○ D) The ability of individuals to adapt to the environment during their lifetime. 7. Which of the following best describes how advantageous traits are passed down in a population? ○ A) Traits are acquired during an individual’s lifetime and passed to offspring. ○ B) Traits are inherited genetically and increase in frequency when they provide a reproductive advantage. ○ C) Traits are not passed down and only affect the individual. ○ D) All traits are equally passed on to future generations. 8. What does it mean when we say a population "changes over generations"? ○ A) The individuals in the population remain the same, but their behavior changes. ○ B) The genetic makeup of the population changes as advantageous traits become more common. ○ C) There are no changes in the population's traits over time. ○ D) The environment of the population remains exactly the same for every generation. 9. Which of the following is an example of how natural selection works in a population?  ○ A) An individual grows taller during its lifetime and passes this trait on to its offspring. ○ B) A population of birds has variation in beak size, and birds with larger beaks survive better during a drought because they can access more food, so this trait becomes more common in future generations. ○ C) All birds in a population have the same beak size, and survival is not influenced by beak size. ○ D) Birds in a population choose mates based only on their color, not their ability to survive. 10. What is the relationship between "advantageous traits" and natural selection? ○ A) Advantageous traits do not affect natural selection. ○ B) Advantageous traits become less common over generations. ○ C) Advantageous traits are selected by nature and increase in frequency in the population. ○ D) Advantageous traits are random and do not influence reproductive success. Answer Key: 1. B) Traits are passed from one generation to the next through genetic inheritance, and individuals differ based on these traits. 2. B) Some individuals survive and reproduce more successfully because of certain traits, such as better camouflage or faster speed. 3. B) The ability of an individual to produce more offspring compared to other individuals in the population. 4. C) By favoring individuals with advantageous traits, leading to an increase in those traits in future generations. 5. B) Traits that improve reproductive success become more common in the population over time. 6. B) Differential reproduction based on inherited traits that affect survival and reproduction. 7. B) Traits are inherited genetically and increase in frequency when they provide a reproductive advantage. 8. B) The genetic makeup of the population changes as advantageous traits become more common.  9. B) A population of birds has variation in beak size, and birds with larger beaks survive better during a drought because they can access more food, so this trait becomes more common in future generations. 10. C) Advantageous traits are selected by nature and increase in frequency in the population. Charles Darwin (1859) conceived the theory of evolution by natural selection, which explains how species adapt and change over time. Darwin observed that beak shape varies among finch species. Variation: the differences that exist between individuals of the same species. Adaptation: the process by which populations become better suited to their environment over time. This variation can be caused by genetic mutations, environmental factors, or a combination of both Divergent evolution: refers to the process by which closely related species evolve into different forms. Convergent evolution: the process by which unrelated species independently evolve similar characteristics in response to similar selective pressures or environmental conditions. Divergent Evolution Convergent Evolution he fossil record provides substantial evidence for evolution by revealing the existence of organisms that lived in the past and the changes in species over time. Transitional Fossils : fossils that exhibit characteristics of both ancestral and descendant species are known as transitional fossils. These fossils provide evidence of gradual evolutionary changes and the transitional stages between different species. Examples include fossils like Tiktaalik, which displays features intermediate between fish and tetrapods, indicating a transition from aquatic to terrestrial life. Extinct Species : the fossil record contains a vast array of extinct species that no longer exist today. The presence of these extinct organisms demonstrates that the Earth has been inhabited by diverse life forms that have evolved and gone extinct over millions of years. Succession of Fossils : fossils found in different layers of rock (strata) can be arranged in a chronological sequence known as the fossil succession. This succession reveals a consistent pattern of species appearing and disappearing in a specific order, demonstrating a temporal progression of life forms. Patterns of Diversity : the fossil record shows a clear pattern of increasing biodiversity over time, with simpler life forms appearing in earlier geological periods and more complex forms evolving in later periods. This pattern is consistent with the predictions of evolutionary theory Transitional form: provides link between earlier and later forms Evolution is just a theory : this misconception arises from a misunderstanding of the scientific usage of the term "theory." In scientific terms, a theory represents a well-supported and extensively tested explanation that encompasses a wide range of observations and evidence. The theory of evolution is backed by abundant evidence from various scientific disciplines, and it provides a comprehensive framework for understanding the diversity and change of life forms over time. Individuals evolve : evolution is a process that occurs at the population level over long periods of time, not within the lifespan of individual organisms. It is the genetic makeup of populations that changes over generations through the mechanisms of mutation, genetic drift, gene flow, and natural selection. Evolution explains the origin of life : the theory of evolution explains the diversification and changes in species over time, but it does not address the origin of life itself. The study of the origin of life, known as abiogenesis , focuses on understanding how life emerged from non-living matter. Evolutionary theory comes into play after the origin of life, explaining how life forms have diversified and adapted through natural processes. Organisms evolved on purpose : evolution is an undirected process. While natural selection can lead to the appearance of purposeful design in organisms, it is a result of the cumulative effects of random genetic variations and the environmental pressures acting upon them. Evolution does not involve a predetermine O1 : Describe the theory of evolution through natural selection. LO4 : Misconceptions about evolution/natural selection LO3 : Sexual selection and sexual dimorphism. LO2 : Different types of natural selection. Natural selection is not random because it involves the differential survival and reproduction of individuals with certain traits that are better adapted to their environment. For example, in a population of peppered moths, individuals with darker wings may have a higher chance of surviving and reproducing in a polluted environment, as they are better camouflaged against soot-covered tree trunks. The frequency of the gene for darker wings increases in the population over time, which is a non-random process driven by the selective pressure of the environment. Natural selection is not progressive because it does not necessarily result in organisms becoming "better" over time. For example, the coelacanth is a primitive fish that has remained relatively unchanged for millions of years, even as other fish species have evolved more complex adaptations. Adaptations are not perfect because they are constrained by various factors such as genetic variation, historical constraints, and trade-offs between competing traits. For example, the human eye has a blind spot where the optic nerve enters the eye because of the way the retina is arranged, which is not an optimal design. Natural Selection 1. A small population of birds flies from the mainland to an island. Birds fed on a variety of different sized seeds on the mainland. 2. Birds produce more offspring than can possibly survive; birds vary in beak size due to genetic differences. 3. Seeds on island are large, so birds with larger beaks are better able to feed. Large beaks are more likely to survive and reproduce than small beaks in this particular environment. 4. Birds in the next generation tend to have larger beaks. This is the result of natural selection. Natural selection is the driving force for evolution. 5. After many generations, genetic changes accumulate, and a new species evolves that is well adapted to the island environment. The theory of evolution through natural selection proposes that species change over time as a result of the differential survival and reproduction of individuals with advantageous genetic traits in response to environmental pressures. Evolution : change in allele frequencies from one generation to the next. Natural selection : some individuals are more successful at survival and reproduction in a particular environment. Fitness : the reproductive success of one individual compared to others in a population. Sexual selection is selection for traits that increase mating success, not necessarily survival. -Disconnect between best fitness strategies: females need to mate with the best males while males need to mate with as many females as possible. Robins typically lay four eggs, an example of stabilizing selection. Larger clutches may result in malnourished chicks, while smaller clutches may result in no viable offspring. Light-colored peppered moths are better camouflaged against a pristine environment; likewise, dark- colored peppered moths are better camouflaged against a sooty environment. Thus, as the Industrial Revolution progressed in nineteenth- century England, the color of the moth population shifted from light to dark, an example of directional selection. In a hypothetical population, gray and Himalayan (gray and white) rabbits are better able to blend with a rocky environment than white rabbits, resulting in diversifying selection. For Example: Sexual dimorphism is phenotypic difference between a population’s males and females. For example: Male peacocks have large feathers compared to female peahens and male ducks have distinct coloring The theory of evolution through natural selection proposes that species change over time as a result of the differential survival and reproduction of individuals with advantageous genetic traits in response to environmental pressures. Evolution : change in allele frequencies from one generation to the next. Natural Selection : some individuals are more successful at survival and reproduction in a particular environment. Fitness : the reproductive success of one individual compared to others in a population. Natural Selection Process in which beneficial traits that are heritable become more common in successive generations. Over time, natural selection results in adaptations : Changes in populations of living organisms that promote their survival and reproduction in a particular environment. Reproductive success Likelihood of an individual contributing fertile offspring to the next generation. Attributed to two categories of traits: Certain characteristics make organisms better adapted and more likely to survive to reproductive age. Traits directly associated with reproduction, such as ability to find a mate and ability to produce viable gametes and offspring. Variation within a given species. Heritable traits can be passed from parent to offspring. Genetic basis was not yet known during Darwin’s time. Natural Selection More offspring are produced than can survive. There is competition for limited resources. Individual with better traits survive and reproduce. Types of Natural Selection 34 In directional selection , selection favors individuals with a phenotype that is different than the norm. Light-colored peppered moths are better camouflaged against a pristine environment and dark- colored moths are better suited to a sooty environment. As the Industrial Revolution progressed in nineteenth century England, the color of the moth population shifted from light to dark. Types of Natural Selection 35 In diversifying selection , two or more extreme phenotypes are favored. Gray and Himalayan (gray and white) rabbits are better able to blend with a rock environment than solid white rabbits. Selection favors the extremes resulting in diversifying selection. Sexual Selection 36 Sexual selection : a specific form of natural selection that operates on traits related to mating success and reproduction. It influences the evolution of populations by selecting for traits that enhance an individual's ability to attract mates and successfully reproduce. Types of Natural Selection 37 Mate Choice : sexual selection involves usually females choosing mates based on certain traits or behaviors. These traits can include physical features, elaborate displays, or behaviors that signal good health, genetic quality, or parental investment. Competition for Mates : sexual selection also involves competition among individuals of the same sex, typically males, for access to mates. This competition can take various forms, such as direct combat, territorial defense, or displays of strength or dominance. Sexual Dimorphism : the situation where males and females of a species differ in physical appearance or behavior. Traits that are advantageous for attracting mates may be more pronounced in one sex compared to the other. For example, male peacocks have elaborate tail feathers for courtship Peacocks and Peahens Argiope appensa spiders Wood ducks Is it Random? 38 Natural selection is not random because it involves the differential survival and reproduction of individuals with certain traits that are better adapted to their environment. For example, in a population of peppered moths, individuals with darker wings may have a higher chance of surviving and reproducing in a polluted environment, as they are better camouflaged against soot- covered tree trunks. The frequency of the gene for darker wings increases in the population over time, which is a non-random process driven by the Is it Progressive? 39 Evolution by natural selection is not progressive because it does not necessarily result in organisms becoming "better" over time. For example, the coelacanth is a primitive fish that has remained relatively unchanged for millions of years, even as other fish species have evolved more complex adaptations. Are Adaptations Perfect? 40 Adaptations are not perfect because they are constrained by various factors such as genetic variation, historical constraints, and trade-offs between competing traits. The retina is a thin, layered tissue at the back of the eye that plays a vital role in vision. The human eye has a blind spot where the optic nerve enters the eye because of the way the retina is arranged. Cephalopod eyes do not have a blind spot because of a different retina arrangement. LO1 : Hardy-Weinberg Principle: a null hypothesis for evolution LO2 : Natural selection, genetic drift, mutation, and non- random mating lead to changes in genotype frequencies LO3 : Gene flow is movement of alleles from one population to another Evolution is a change in allele/genotype frequencies in a population over time. The Hardy-Weinberg principle of equilibrium states that the frequencies of alleles in a large, randomly mating population will remain constant from generation to generation in the absence of disturbing influences such as mutation, gene flow, selection, and genetic drift. The Hardy-Weinberg principle provides a null hypothesis against which to test for evolutionary changes in populations. LO4 : Genetic drift is random fluctuation in allele frequencies Other methods of evolution and Hardy-Weinberg Static allele frequencies assume: 1. Infinitely large population size 2. No selective pressure against a trait 3. No migration: no exchange of alleles between populations. 4. No mutation 5. Random mating LO5 : Mutations drive evolution These conditions are NEVER met in nature! Natural Selection Green beetles are easy for birds to see. Brown beetles are more likely to survive to produce offspring. Those offspring are also brown; thus, the subsequent generation has a higher % of brown beetles than before. Genetic Drift By chance, several green beetles were killed when someone stepped on them, thus leaving more brown beetles to reproduce. As a result, the next generation has a higher % of brown beetles than the previous generation. Mutation A mutation leads to the formation of a new allele (and thus new genotype) that produces blue beetle. The beetle population’s genotype frequency is altered. Non-random mating Brown beetles prefer mating with only brown beetles. This leads to changes in the genotypes of next generation, as more brown beetles are produced. The movement of alleles into or out of a population is referred to as gene flow. In this case, a brown beetle is moving into a population of only green beetles, and the genetic diversity is increasing in the recipient population. However, if there were equal gene flow between the populations, as in geographically continuous populations, the two populations would become more homogenous. Gene flow is random with respect to fitness. Founder effect – few individuals found new population Bottleneck effect – drastic reduction in population and thus size of gene pool Genetic drift involves random changes in allele frequency. It is sometimes referred to as sampling error. It occurs in all populations in every generation, but it has a stronger effect on smaller populations. It can lead to the permanent loss of some alleles and the fixation of others, decreasing genetic diversity in a population. Genetic drift is random with respect to fitness. Mutations are permanent changes in the DNA that create new alleles, and when they occur in gametes and are passed to offspring, they increase genetic diversity Mutations are random with respect to fitness. Most mutations are deleterious, and eliminated by selection Rarely, a mutation creates a beneficial allele that will increase in frequency in a population due to natural Mutation in Rock Pocket mouse causes black fur, which is favorable in this environment. What do you predict will happen to the population after several generations? Hardy-Weinberg A Null Hypothesis for Evolution 45 The Hardy-Weinberg principle : is a fundamental concept in population genetics that describes the relationship between allele and genotype frequencies in a fixed population. According to the principle, in a large, randomly mating population that is not subject to evolutionary forces, the frequencies of alleles and genotypes will remain constant from generation to generation. The principle states that the frequencies of alleles in a population will remain the same (p+q=1) and the frequencies of genotypes will remain the same (p2+2pq+q2=1), where p and q represent the frequencies of the two alleles at a given locus. The Hardy-Weinberg principle provides a null hypothesis against which to test for evolutionary changes in populations. Hardy-Weinberg A Null Hypothesis for Evolution 46 Homozygous ( GG ) 36% Heterozygous ( Gg ) 48% Homozygous Recessive ( gg ) 16% Genotype Frequencies Genotypes Phenotypes # Frogs GG Dark Green 36 Gg Dark Green 48 gg Light Green 16 Alleles Calculati on # Alleles G 36+36+ 48 120 g 16+16+ 48 80 Hardy Weinberg Principle states these DO NOT change from generation to generation Hardy-Weinberg Assumptions 47 The Hardy-Weinberg principle states that the frequencies of alleles in a population will remain constant from generation to generation in the absence of evolutionary influences such as mutation, migration, selection, and genetic drift. Static allele frequencies assume: 1. No selective pressure against a trait 2. No mutation: alleles do not change. 3. No migration: no exchange of alleles between populations. 4. Infinite population size. 5. Random mating. Mechanisms of Evolution 48 Natural selection: finally, the most famous mechanism of evolution! Natural selection occurs when one allele (or combination of alleles of different genes) makes an organism more or less fit, that is, able to survive and reproduce in a given environment. If an allele reduces fitness, its frequency will tend to drop from one generation to the next. Mechanisms of Evolution 49 Mutation : Although mutation is the original source of all genetic variation, mutation rate for most organisms is pretty low. So, the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large. However, natural selection acting on the results of a mutation can be a powerful mechanism of evolution! Mechanisms of Evolution 50 Gene flow : involves the movement of genes into or out of a population, due to either the movement of individual organisms or their gametes (eggs and sperm, e.g., through pollen dispersal by a plant). Organisms and gametes that enter a population may have new alleles, or may bring in existing alleles but in different proportions than those already in the population. Gene flow can be a strong agent of evolution. Mechanisms of Evolution 51 Non-infinite population size (genetic drift): genetic drift involves changes in allele frequency due to chance events – literally, "sampling error" in selecting alleles for the next generation. Drift can occur in any population of non-infinite size, but it has a stronger effect on small populations. We will look in detail at genetic drift and the effects of population size. Mechanisms of Evolution 52 Non-random mating : In non-random mating, organisms may prefer to mate with others of the same genotype or of different genotypes. Non-random mating won't make allele frequencies in the population change by itself, though it can alter genotype frequencies. This keeps the population from being in Hardy-Weinberg equilibrium, but it’s debatable whether it counts as evolution, since the allele frequencies are staying the same. Types of Drift Bottleneck Effect 53 Population is dramatically reduced due to some environmental event (volcanic eruption) The genetic diversity is reduced, commonly lose an allele(s) Types of Drift Founder Effect 54 A few members of a population leave and start a new population The genetic diversity is reduced, commonly lose an allele(s)