BIO 112 Chapter 23 PDF

**23.1 Genes in Populations** **Learning Outcomes:** **1. Define a gene pool.** - All of the alleles for every gene in a given population make up the gene pool **2. Distinguish allele frequency and genotype frequency.** 3\. (do not need to know) **4. List the conditions that must be met...

**23.1 Genes in Populations** **Learning Outcomes:** **1. Define a gene pool.** - All of the alleles for every gene in a given population make up the gene pool **2. Distinguish allele frequency and genotype frequency.** 3\. (do not need to know) **4. List the conditions that must be met for a population to be in Hardy-Weinberg equilibrium.** - the Hardy-Weinberg equation requires five conditions: (1) no new mutations occur to alter allele frequencies. (2) no natural selection occurs; that is, no survival or reproductive advantage exists for any of the genotypes. (3) the population is so large that allele frequencies do not change due to random chance. (4) no migration occurs between different populations, altering the allele frequencies. (5) random mating occurs; that is, the members of the population mate with each other without regard to their genotypes. **5. Describe the factors that cause microevolution to occur** - there are two phenomena that cause microevolution to occur: (1) the introduction of new genetic variation into a population; these include new mutations within genes that produce new alleles, gene duplication, and horizontal gene transfer. (2) one or more mechanisms that alter the prevalence of a given allele or genotype in a population; examples of this include natural selection, genetic drift, migration, and nonrandom mating **Key Terms:** **Population genetics** -- study of genes and genotypes in a population **Gene pool** -- all of the alleles for every gene in a given population **Polymorphism** -- refers to the presence of two or more variations for a given character within a population **Polymorphic gene** -- a gene that commonly exists as two or more alleles in a population **Monomorphic gene** -- a gene that predominantly exists as a single allele in a population **Population** -- a group of individuals of the same species that occupy the same environment at the same time and, for sexually reproducing organisms, can interbreed with one another **Single-nucleotide polymorphism (SNP)** -- a type of genetic variation in a population in which a particular gene sequence varies at a single nucleotide **Personalized medicine** -- a medical practice in which information about a patient's genotype is used to tailor that person's medical care **Allele frequency** -- in a population the number of copies of a specific allele in a population divided by the total number of all alleles for that gene in the population **Genotype frequency** -- in a population, the number of individuals with a given genotype divided by the total number of individuals **Microevolution** -- changes in a population's gene pool, such as changes in allele frequencies, from generation to generation **Notes:** - Each member of a population receives its genes from its parents, which contributes to the given gene pool of the next generation. - Populations vary from generation to generation, such as size and geographic location; this can lead to the genetic composition changing as well - Polymorphism describes the variation in the DNA sequence of genes; there are polymorphic genes and monomorphic genes - A polymorphism can be a result of changes like a deletion of a significant region of the gene, a duplication of a region, or a change in a single nucleotide - SNPs (or snips) are the smallest type of genetic variation in a given gene and the most common; an example is the sickle cell allele -- the non-disease-causing allele and the sickle cell allele represent a SNP of the β-globin gene - Variations in SNPs are associated with how people respond to viruses, drugs, and vaccines - An approach to analyze genetic variation in populations is to consider the frequency of specific alleles and genotypes quantitively - In 1908, Godfrey Harold Hardy and Wilhelm Weinberg independently derived a simple mathematical expression that describes the relationship between allele and genotype frequencies in a population - The validity of the Hardy-Weinberg equation rests on the assumption that two gametes combine randomly to produce offspring **23.2 Natural Selection** **Learning Outcomes** **1. Explain how natural selection can result in a population that better adapted to its environment and more successful at reproduction**. - Natural selection can result in a population that is better adapted to its environment because some individuals in a population have greater reproductive success, and those individuals are likely to pass the heritable traits that favor reproductive success are more likely to pass those traits to their offspring - There are to categories of traits are commonly attributed to reproductive success: (1) certain characteristics that make an organism better adapted to their environment, therefore more likely to survive to reproductive age. (2) reproductive success involves traits like the ability to find a mate and produce viable gametes and offspring; an example of this is the brightly colored plumage in male birds which are often subject to natural selection 2\. Calculate the fitness values of given genotypes (not necessary) **3. List and distinguish the four different patterns of natural selection** - There are four different patterns of natural selection: (1) directional selection, which is when individuals at one extreme of a phenotypic range have greater reproductive success in a particular environment. (2) stabilizing selection, which favors the survival of individuals with intermediate phenotypes and selects against those with extreme phenotypes. (3) diversifying selection (or disruptive selection) favors the survival of two or more different genotypes that produce different phenotypes, and is more likely to occur in populations that occupy heterogeneous environments. (4) balanced selection occurs when a genetic diversity is maintained in a population **Key Terms:** **Natural selection** -- the process by which individuals with certain heritable traits tend to survive and reproduce at higher rates than those without those traits **Adaptations** -- changes in populations of living organisms that increase their ability to survive and reproduce in a particular environment **Reproductive success** -- the likelihood of an individual contributing fertile offspring to the next generation **Fitness** -- the relative likelihood that one genotype will contribute to the gene pool of the next generation compared with other phenotypes **Mean fitness of the population** -- the average reproductive success of members of a population **Directional selection** -- a pattern of natural selection that favors individuals at one extreme of a phenotypic distribution **Stabilizing selection** -- a pattern of natural selection that favors the survival of individuals with intermediate phenotypes and selects against those with extreme phenotypes **Diversifying selection** -- a pattern of natural selection that favors the survival of two or more different genotypes that produce two or more different genotypes that produce different phenotypes **Balancing selection** -- a pattern of natural selection that maintains genetic diversity in a population **Balanced polymorphism** -- the phenomenon in which two or more alleles are kept in balance and maintained in a population over the course of many generations **Heterozygote advantage** -- a phenomenon in which a heterozygote has a higher fitness than either corresponding homozygote **Negative frequency-dependent selection** -- a pattern of natural selection in which the fitness of a genotype decreases when its frequency becomes higher; the result is balanced polymorphism **Notes:** - The modern description of natural selection contributes to the knowledge of molecular genetics to the process of evolution: - Within a population, allelic variation arises from random mutation that cause differences in DNA sequence of the encoded protein, which may alter the protein's function - Some alleles encode proteins that enhance an individual's survival or reproductive capability over that of other's within a population; an example is an allele that produces a protein that is more efficient at a higher temperature, increasing the survival of an individual in a hot climate - Individuals with beneficial alleles are more likely to survive and contribute their alleles to the gene pool of the next generation - Over generations, allele frequencies of many different genes may change through natural selection, which significantly alters the characteristics of a population - Fitness is a quantitative measure of reproductive success -- so an extremely fertile individual has a higher fitness than a less fertile individual that appears more physically fit. - Directional selection is commonly caused by a population that is exposed to a prolonged change in its living environment, which may cause the relative fitness values to change in favor of a specific genotype, therein promoting the elimination of other genotypes - An example of heterozygote advantage is the *H^S^* allele of the human β-globin gene; when someone is homozygous for *H^S^H^S^*, they have sickle cell disease; this person has a lower fitness than a homozygote with two copies of *H^A^H^A^*, which is the common β-globin gene. If someone is *H^A^H^S^* they do not typically have symptoms of the disease, but they have increased resistance to malaria *(\*isn't that crazy!)* so someone who is heterozygous has a higher fitness, because they do not show symptoms for sickle cell disease, and have increased resistance to the malarial parasite. **23.3 Sexual Selection** **Learning Outcomes** **1. Define sexual selection** - Sexual selection is a form of natural selection in which individuals with certain traits are more likely to engage in successful reproduction than other individuals **2. Distinguish between intrasexual and intersexual selection** **3. Analyze the results of Seehausen and Van Alphen, and explain how they relate to sexual selection.** **Key Terms:** **Notes:** **23.4 Genetic Drift** **Learning Outcomes** **1. Define genetic drift, and explain its effects on allele frequencies over time** **2. Compare and contrast the bottleneck and founder effects.** **3. Explain how neutral mutations can spread through a population** **Key Terms:** **Notes:** **23.5 Migration and Nonrandom Mating** **Learning Outcomes** **1. Describe how gene flow affects genetic variation in neighboring populations.** **2. Define inbreeding, and explain how it may have detrimental consequences.** **Key Terms:** **Notes:** BIO 112 In class Chapter 23 **1. All of the alleles for every gene in a population constitutes the-** a. Genome b. Community c. **gene pool** d. population e. Species **2. A group of conspecifics that occupy the same habitat and can interbreed with each other form a-** a. species b. community c. gene pool d. **population** e. genome **3. Most of the genetic diversity seen in human populations is due to single nucleotide polymorphisms.** a. **this is true** b. this is false **4. Which of the following is NOT an assumption of the Hardy-Weinberg equilibrium?** \*[know all five assumptions] a. Very large population size b. Random mating c. No gene flow d. No mutations e. **All are assumptions** **5. The merging of 2 formally separated populations would be an example of-** a. Mutation b. Natural selection c. Bottleneck d. **Gene flow** e. Random mating **6. If a population is drastically reduced in size and rebounds what has occurred?** a. Mutation b. Natural selection c. **Bottleneck** d. Gene flow e. Random mating **7. What is fitness?** a. **A measure of reproductive success** b. The rate of survival of a species c. A measure of an animal's top seed d. A measure of the overall size of an individual **8. The display feathers of a peacock are an example of-** a. Gene flow b. Mutation c. **Sexual selection** d. Random mating e. Genetic drift **9. Genetic changes that do not affect reproductive success are examples of neutral variation.** a. **This is true** b. This is false **10. Due to the increased likelihood of deleterious homozygous recessive phenotypes, what can occur when closely related individuals mate and form offspring?** a. Genetic drift b. **Inbreeding depression** c. Sexual selection d. Random mating e. Gene flow **11. The allele frequencies in a population are p = 0.95 and q = 0.05. What would happen to the allele frequency of q if the population followed the Hardy-Weinberg equilibrium for 20 generations.** **\* not going to have math on exam or** a. Increase b. Decrease c. **Remain the same** d. Change randomly e. None of the above **13. The mean beak depth of a particular finch species is 15 millimeters. Assuming the trait is heritable what would happen to the mean claw length after several generations of stabilizing selection?** a. The mean should be less than 15mm b. The mean should be greater than 15mm c. **The mean should not change** d. The population should diverge with respect to\ beak depth **15. A population of freshwater fish has been drastically reduced in size due to the construction of a dam. The dam is removed and the population numbers\ rebound, what has happened to the genetic variability in this population?** a. Increased b. **Decreased** c. Remains the same **16. Male Anolis lizards use dewlap displays to attract females to attract females. If in a single species males with darker colored dewlaps tend to display in open habitats and males with lighter colored dewlaps tend to display in more forested habitats\ the resulting offspring may start to diver into 2 groups. What would be occurring?** a. Random mating b. Directional selecting c. Hardy-Weinberg equilibrium d. **Diversifying selection** e. Neutral variation **17. Descent with modification refers to-** a. Natural selection b. **Evolution** c. Artificial selection **18. Which of the following are assumptions of the Hardy-Weinberg equilibrium?** a. No mutation b. No gene glow c. Large population size with random mating d. No selection e. **all of the above assumptions of the equilibrium** **19. If a population is drastically reduced in size and rebounds what has occurred?** a. Mutation b. Natural selection c. **Bottleneck** d. Gene flow e. Random mating **20. Differential reproduction under natural conditions is-** a. Hardy-Weinberg equilibrium b. Artificial selection c. **Natural selection** d. Mutation e. Genetic drift **21. Negative frequency dependent selections acts to favor the most common phenotype in a population.** a. this is true b. **this false** **22. Which form of selection would tend to push the mean value of a trait to one extreme?** a. stabilizing b. **disruptive** c. directional d. oscillating e. bimodal **23. a small subset of the large population that colonizes a new habitat is an example of genetic drift.** a. **this is true** b. this is false **24. Acquired traits are passed onto offspring.** a. This is true b. **this is false** **25. Which of the following must be true in order for selection to occur?** a. Genetic variation must exist in a population b. Genotypic differences must reflect phenotypic differences c. Variation must be heritable d. Variation results in different numbers of surviving offspring e. **All of the above must be true for selection to occur** **26. If all of the assumption of the Hardy-Weinberg equilibrium were met, what would happen to the frequency of the recessive allele after many generations of mating?** a. Increase b. Decrease c. **remain the same** d. It depends on the starting frequencies **27. The mean claw length of a particular crab species is 35 mm. Assuming the trait is heritable what would happen to the mean claw length after several generations of stabilizing selection?** a. The mean should be less than 35 mm b. The mean should be greater than 35mm c. **the mean should not change** d. the population should diverge with respect for claw length **28. Albino alligators are rare in the wild due to a lack of.....** a. **Positive frequency dependent selection** b. Sexual selection c. Artificial selection d. Stabilizing selection e. Heterozygote selection **30. How do negative frequency dependent selection oscillating selection, and heterozygote selection affect genetic variation in populations?** a. They act to reduce overall diversity b. **they act to maintain genetic diversity** c. They select for a single phenotype d. They form new and novel phenotypes e. None of the above