Hardy Weinberg Equilibrium

What is Hardy-Weinberg equilibrium? Watch this video as an intro. Intro-Hardy-Weinberg equilibrium describes populations that have their gene pools at equilibrium or in balance and unchanging. The Hardy-Weinberg principle quantifies and gene pool- the genetic info of an entire population- by measuring a population's allele frequency and determining if it is changing over time. A population that has allele frequencies that do not change (at equilibrium) are not evolving, whereas a population whoses allele frequency is changing is said to be evolving. To determine if the change is significant enough to say that evolution is happening a second test must be done- the Chi-Squared Test. Biologists often use models to learn more about complex situations. Hardy-Weinberg equilibrium is a model that can be used to study how a population is changing. It was developed in 1908 and is named after the two people who developed it, G.H Hardy (a mathematician) and Wilhelm Weinberg (Obstetrician). Here, equilibrium refers to genotype and allele frequencies that stay the same from generation to generation. If genotype and allele frequencies of a population stay in equilibrium then the population is not evolving. Populations that meet five conditions listed below are said to be in Hardy-Weinberg equilibrium; meaning they are not evolving. Allele frequency doesn't change if:• There is a very large population. Large populations are stable and no genetic drift will occur.• No emigration or immigration. No gene flow can occur.• No mutations. No new alleles can be added to the gene pool.• Random mating. Everyone has the choice with whom to mate. No artificial selection. No sexual selection can occur.• No natural selectionAll traits must equally help in survival. Real populations rarely meet all five conditions. But the model is a useful tool for understanding changes in populations. Real data can be compared with data predicted by the model. What does is mean if a population meets all five conditions listed above? What are the rules and equations we need to know? Rules: These will make sense in a minute.1. Always work with "q" first because it represents the recessive allele and we can observe that phenotype in the population being studied.2. If you are given a % for something it is the q2. There if you are given that black is dominant to brown, and there are 20% brown it represents the q2. In order to get the q you need to change it to decimal form (.20) and take the square root. Therefore, q= 0.45EquationsAllele Frequency: p + q= 1p represents the frequency of the dominant allele and q represents the frequency of the recessive allele.Genotype Frequency: p2 + 2pg +q2 = 1p2 represents the frequency of the homozygous dominant genotype2pq represents the frequency of the heterozygous genotype.q2 represents the frequency of the homozygous recessive allele. The Hardy-Weinberg equation is used to predict allele and genotype frequencies in a population. The Hardy-Weinberg equation can be used to predict allele and genotype frequencies for simple dominant-recessive traits in a population. The equation predicts the values that would be present if the population is in equilibrium.Let’s use the Hardy-Weinberg equation to calculate predicted genotype frequencies for a tail shape trait in a population of 1000 fish.• 640 fish have forked tail fins, which is the dominant trait. Forked-fin fish have TT or Tt genotypes.• 360 fish have smooth tail fins, and the homozygous recessive tt genotype.The letter p stands for the frequency of the dominant allele and q stands for the frequency of the recessive allele. The Hardy-Weinberg equation is: What do p and q stand for in the Hardy-Weinberg equation ? There are five factors that can lead to evolution. In nature, evolution should be expected in all populations most of the time. The Hardy-Weinberg model shows there are five factors that can lead to evolution.Evolution is continuous. Environments are always changing, although often very slowly relative to a human’s lifetime. Evolution is a response to these changes. As environments change, populations either adapt or go extinct. When a population becomes extinct, a different species can take its place, and the cycle continues. What are five factors that can lead to evolution? What does it mean for a population to be in Hardy-Weinberg equilibrium? Is it common for natural populations to be in Hardy-Weinberg equilibrium? Explain. In a population of organisms, the frequency of the homozygous recessive genotype is 0.3, the frequency of the heterozygous genotype is 0.6, and the frequency of the homozygous dominant genotype is 0.1. Fill in the correct numbers for each variable below:p22pqq2 Lets walk through a question step by step.Question: In a particular type of flower, red petals (R) are dominant to white petals (r). We observe that 480 of the 500 flowers have red petals, and 20 of the 500 flowers have white petals. What are the allele and genotype frequencies for this population of flowers? Which set of data do you always start with? Dominant phenotype data Recessive phenotype data What is the q value? Always work with the q first because the p can be RR or Rr and we can't tell the difference by looking at them. 0.04 0.2 The p value is calculated by p + q = 1 .96 0.8 How do we determine the genotype frequency? Now we can use the allele frequency to determine the genotype frequencies by imputing the values for p and q into the genotype frequency equation- p2 + 2pq +q2 = 1.The frequency of the homozygous dominant genotype is p2The frequency of the heterozygous genotype is 2pqThe frequency of the homozygous genotype is q2 The frequency of homozygous individuals in the plant population is 0.92 0.64 . 45 The frequency of heterozygous individuals is 0.32 0.08 .45 The frequency of the recessive allele is 0.35 0.04 0.2 TRY THIS! Try one on your own now- A large population of 400 individuals has 393 individuals expressing a dominant phenotype. What are the allele and genotype frequencies? Report your answer below like this:p=q=p2=2pq=q2= Extra help with allele frequency Extra help with Hardy Weinberg equilibrium More practice will be coming shortly in another sheet. Example