Lecture 2: Population Genetics PDF

# Lecture 2: Population Genetics ## Lecturer: Dr. Hadil Alahdal A colorful spiral design is in the background. An oval with white text on a gray background reads "Lecture 2: Population Genetics" ## Overview The document is a presentation about the mechanics of population genetics. It covers t...

# Lecture 2: Population Genetics ## Lecturer: Dr. Hadil Alahdal A colorful spiral design is in the background. An oval with white text on a gray background reads "Lecture 2: Population Genetics" ## Overview The document is a presentation about the mechanics of population genetics. It covers the following topics: - Genetic Variation - Allele Frequencies - Hardy-Weinberg Equilibrium - Evolutionary Forces - Natural Selection - Genetic Drift - Gene Flow - Adaptation and Fitness - Speciation - Conservation Genetics ## Explore More A graphic of 3 figures with DNA connecting them is in the background. The text on the page says "Explore the foundational concepts of evolutionary genetics, from the mechanisms of genetic variation to the forces that shape allele frequencies. Learn how these principles drive the adaptation and diversification of species over time." ## Lectures outline * **Genetic Variation:** - Mechanisms that generate genetic diversity within a population, including mutation, recombination, and gene flow. * **Allele Frequencies:** - How allele frequencies change over time due to evolutionary forces like selection, drift, and migration. * **Hardy-Weinberg Equilibrium:** - The mathematical model that describes the expected genotypic and allelic frequencies in a population under certain assumptions. * **Evolutionary Forces:** - The key drivers of evolution, including natural selection, genetic drift, and gene flow, and how they impact genetic diversity. * **Adaptation and Fitness:** - How genetic variation enables organisms to adapt to their environment, and the concept of reproductive fitness. * **Speciation:** - The processes by which new species arise, including geographic isolation, reproductive barriers, and adaptive radiation. * **Conservation Genetics:** - How evolutionary genetics principles are applied to conserve genetic diversity and protect endangered species. ## The Wolves of Isle Royale A photo shows a wolf in the snowy wilderness - Page: 1149 - Link to a PDF: file:///C:/Users/al_ma/Downloads/Genetics%20A%20Conceptual%20Approach%20by%20Pierce,%20Benjamin%20A.%20(z-lib.org)%20(1).pdf ## Wolf Pedigree The document displays a pedigree showing the lineage of wolves. The pedigree is a branching graph like this: * Old Guy - Unknown Female - Unknown Female - Unknown Male - Unknown Female - Unknown Male - Unknown Male - Unknown Female - Unknown Male - Unknown Female - Unknown Male - Unknown Male - Unknown Female - Unknown Female - Unknown Female - Unknown Male - Unknown Female - Unknown Female - Unknown Female - Unknown Female - Unknown Female - Unknown Male - Unknown Female - Unknown Male - Unknown Male - Unknown Female - Unknown Female - Unknown Female - Unknown Female - Unknown Female - Unknown Female - Unknown Male - Unknown Female - Unknown Male - Unknown Male ## Conservation Genetics Three images portray "Preserving Genetic Diversity", "Ensuring Species Survival", and "Genetic Analysis." - **Preserving Genetic Diversity:** Concentration genetics focuses on maintaining healthy gene pools and preventing the loss of genetic variation within endangered populations. - **Ensuring Species Survival:** Strategies are employed to protect genetic diversity and avoid the harmful effects of inbreeding, allowing endangered species to thrive. - **Genetic Analysis:** Advanced genetic analysis techniques are used to monitor populations and guide conservation efforts to preserve critical genetic diversity. ## Conservation Genetics: In Action A photo shows a scientist using a pipet in a lab setting. Text below describes the ways that genetic information is used to guide conservation. <start_of_image>- **Genetic Monitoring:** Tracking genetic diversity over time. - **Population Management:** Designing strategies for species recovery - **Habitat Connectivity:** Maintaining gene flow between populations. - **Evolutionary Adaptation:** Understanding how species adapt to environmental change. ## Genotype and Allele Frequencies Two pictures are on this slide. One shows a stadium full of people, and the other shows a clump of lady bugs. - **Genotypic and Allelic Frequencies are Used to Describe the Gene Pool of a Population:** Population genetics is a field of study that focuses on the genetic makeup of populations and how it changes over time. The genetic makeup of a population, known as its gene pool, is represented by the frequencies of genotypes and alleles. ## Population Genetics: Uncovering Genetic Variation Two images are on this slide. One shows a 3D image of double helix DNA. The other shows a close up of a microscope. - **Understanding Genetic Variation:** Population genetics studies how genetic variation changes within and between populations over time. - **Fundamental for Research:** This field is fundamental for understanding evolution, conservation, and human health. ## Inbreeding A photo of three people standing close together is in the background. Below is a list of effects of inbreeding. - **Inbreeding is the mating of closely related individuals. It can lead to a decrease in genetic diversity and an increase in the frequency of harmful recessive alleles** - Reduced Fitness: Increased vulnerability to diseases and environmental stresses. - Increased Genetic Load: Accumulation of harmful recessive alleles. - Inbreeding Depression: Reduced fertility, survival, and overall fitness. ## Mutation: The Driving Force of Genetic Diversity Three pictures are on this page, showing a lab setting, a scientist in protective gear, and a green leafy plant. - **Spontaneous Mutations:** Unintended changes in the DNA sequence that occur naturally during replication, introducing new genetic variation. - **Induced Mutations:** External factors like radiation or chemicals can disrupt DNA replication, leading to errors and genetic changes. - **Beneficial Mutations:** Mutations that improve an organism's chances of survival and reproduction, providing the raw material for evolution. ## Mutation: The Driving Force of Genetic Diversity 2 Two pictures are on this slide. One shows a stylized image of DNA. The other shows DNA surrounded by colorful dots. - **Deleterious Mutations:** Genetic changes that reduce an organism's fitness and overall well-being, often targeted by natural selection. - **Neutral Mutations:** DNA changes that neither improve nor reduce an organism's fitness, but are important for tracing evolutionary history. ## Gene Flow A map displays the world in black and white. In black, the map shows the movement of genes between populations. - **Gene flow is the movement of genes between populations. It can increase genetic diversity and prevent populations from becoming isolated.** - **Migration:** Movement of individuals between populations. - **Interbreeding:** Introduction of new alleles and mixing of gene pools. - **Reduced Genetic Drift:** Counteracts the effects of random allele frequency changes. - **Increased Adaptation:** Promotes the spread of advantageous alleles. ## Evolutionary Biology: Speciation Three pictures are on this page. One shows a small, brown animal with a large tail and a bird. The next photo shows a misty, forested mountain overlooking water, with a human figure in the foreground. The third photo shows a small dog, several trees and plants, and a deer in the background. - **The process of speciation:** Speciation is the process by which new species arise, often through the development of reproductive barriers that lead to the divergence of populations over time. - **Mechanisms of Speciation:** Speciation can occur through a variety of mechanisms, such as geographic isolation, adaptation to different environments, or the emergence of genetic incompatibilities. - **Importance for Biodiversity:** The study of speciation is crucial for understanding the origins of biodiversity and the evolutionary trajectories of different lineages. ## Allele Frequencies Three pictures are on this page. One shows a line graph outlining the frequency of alleles over time. The next photo shows two test tubes containing blue and red liquids that have been held together. The last photo shows a stylized graphic of a network of circles interacting with each other - **Allele Frequencies: A Numerical Representation:** The frequency of an allele is its proportion within the gene pool. - **From 0 to 1:** Allele frequencies are represented as decimals, ranging from 0 to 1. An allele frequency of 0 indicates the allele is not present in the population, while a frequency of 1 means all individuals carry that allele. - **Dynamic Frequencies:** Allele frequencies change over time, driven by factors such as mutation, gene flow, and genetic drift. ## The Hardy-Weinberg Law Describes the Effect of Reproduction on Genotypic and Allelic Frequencies - **The primary goal of population genetics is to understand the processes that shape a population's gene pool.** - We must ask what effects reproduction and Mendelian principles have on the genotypic and allelic frequencies. - How do the segregation of alleles in gamete formation and the combining of alleles in fertilization influence the gene pool? - **The answer to this question lies in the Hardy-Weinberg law, among the most important principles of population genetics.** ## The Hardy-Weinberg Law A table displays the expected combinations of alleles and the frequencies of the genotypes. The law is actually a mathematical model that evaluates the effect of reproduction on the genotypic and allelic frequencies of a population. It makes several simplifying assumptions about the population and provides two key predictions if these assumptions are met. For an autosomal locus with two alleles, the Hardy-Weinberg law can be stated as follows: - **Assumptions**: If a population is large, randomly mating, and not affected by mutation, migration, or natural selection, then: - **Prediction 1**: The allelic frequencies of a population do not change. - **Prediction 2**: The genotypic frequencies stabilize (will not change) after one generation in the proportions p (the frequency of **AA**), 2pq (the frequency of **Aa**), and q (the frequency of **aa**), where p equals the frequency of allele **A** and q equals the frequency of allele **a**. ## Hardy-Weinberg Assumption <start_of_image>- First, it assumes that the population is large. - Second assumption of the Hardy-Weinberg law is that members of the population mate randomly with respect to genotype. - The third assumption of the Hardy-Weinberg law is that the allelic frequencies of the population are not affected by natural selection, migration, or mutation. - A final point is that the assumptions of the Hardy-Weinberg law apply to a single locus - **Hardy-Weinberg Equation:** p2 + 2pq + q2 = (p +q)2 ## Example: - If there are only 2 alleles at a locus and the dominant is at frequency 0.3, what is the frequency of heterozygotes and how do you figure it out? - You can figure it out by making use of the Hardy-Weinburg equation which is p+q=1. - Let's say p is the frequency of 0.3 and we are looking for the frequency of q. - p+q=1 - 0.3 + q = 1 - q = 0.7 or 70% ## Concept Check Which statement is not true about Hardy-Weinberg law: - The allelic frequencies of (p and q) are equal - The population is large. - The members of the population mate randomly with respect to genotype. - The allelic frequencies of the population are not affected by natural selection ## Genetic Diversity Four images are on this slide. Each shows an animal with different features: a brown antelope, a spotted antelope, a brown antelope with long horns, and a white antelope. - **Genetic diversity refers to the variation in genes within a population. It is crucial for a population's adaptability and resilience to environmental changes** - **Adaptability:** High genetic diversity allows populations to adapt to changing environments and survive threats. - **Resilience:** Genetic diversity safeguards against the risk of extinction caused by disease, climate change, or other disturbances. - **Evolution:** Genetic variation is the raw material for evolutionary change. - **Conservation:** Protecting genetic diversity is essential for preserving biodiversity and ensuring the long-term health of ecosystems. ## Factors Affecting Genetic Diversity Three pictures are presented. The first is a graph showing the change in frequency of alleles over time. The second photo shows people walking through a field. The third photo shoes a cluster of colorful flowers. - **Genetic Drift:** Random fluctuations in allele frequencies, especially in smaller populations, can lead to changes in the genetic makeup over time. - **Gene Flow:** The movement of individuals between populations introduces new alleles and alters the allele frequencies, increasing genetic diversity. - **Natural Selection:** Differential survival and reproduction based on traits influenced by genes. It favors advantageous alleles and eliminates disadvantageous ones, shaping the genetic diversity of a population ## Genetic Drift On this page is a photo of six butterflies, all with different patterns and coloration. The text explains the ways that allele frequency can shift, including the founder effect and the bottleneck effect. <start_of_image>- **Genetic drift is the random fluctuation of allele frequencies within a population over successive generations. This process is especially significant in smaller populations, where the effects of chance events can have a more pronounced impact on the genetic makeup of the group.** - **Founder Effect:** A new population is established by a small group of individuals from a larger population. This can lead to a loss of genetic diversity, as the random sampling of alleles from the original population may not be representative of the full diversity present. Over time, the founder population can diverge significantly from the source population due to this random sampling effect. - **Bottleneck Effect:** A drastic reduction in population size due to a catastrophic event, such as a natural disaster, disease outbreak, or human-caused environmental degradation. The surviving population may have a limited gene pool, leading to a loss of genetic diversity. This can make the population more vulnerable to future threats and reduce its ability to adapt to changing conditions. ## The Effects of Genetic Drift - **Genetic drift is a random process that can have significant effects on the genetic makeup of a population over time. The key effects of genetic drift:** - **A change in allelic frequencies** - **Reduced of genetic variation within a population. (Fixation)** - **Different population diverge genetically with time** - The first two factors tack place within population, and the third is between populations ## Genetic Drift Explained A graph on this slide shows the allele frequency of four populations over time. - **Genetic drift is a random process that can have significant effects on the genetic makeup of a population over time. It occurs due to the random sampling of alleles during reproduction, which can lead to changes in allele frequencies from one generation to the next.** - **Genetic drift can also occur between different populations of the same species. When populations become isolated from one another, random changes in allele frequencies can lead to those populations diverging genetically over time. This is known as interpopulation genetic drift.** ## Several Evolutionary Forces Can Cause Changes in Allelic Frequencies - **Natural Selection:** Natural selection is the process by which individuals with advantageous traits are more likely to survive and reproduce, passing on those traits to future generations. This drives the adaptation of species over time. Natural selection acts on the phenotypes of individuals - the observable physical and behavioral characteristics that result from the interaction of an organism's genotype and its environment. Individuals with phenotypes that are better adapted to their environment will have a higher fitness, meaning they are more likely to survive and reproduce. This in turn leads to an increase in the frequency of the corresponding genotypes in the population over time. ## Summary - These evolutionary forces affect both genetic variation within populations and genetic divergence between populations. - Evolutionary forces that increase genetic variation within populations are listed. These forces include some types of natural selection, such as overdominance, in which both alleles are favored. Mutation and migration also increase genetic variation within populations, because they introduce new alleles into the population. - Evolutionary forces that decrease genetic variation within populations are listed in the lower left quadrant. These forces include genetic drift, which decreases variation through the fixation of alleles, and some forms of natural selection, such as directional selection. ## References - https://www.khanacademy.org/science/ap-biology/natural-selection/hardy-weinberg-equilibrium/v/allele-frequency - https://www.biologyonline.com/dictionary/genetic-diversity