welcome to ap daily this is mr burris from union high school in vancouver washington today's topic is 7.5 hardy-weinberg equilibrium so what will we be learning today for today's lesson we're going to look at what is the hardy-weinberg model what are the conditions under which allele and genotype frequencies will change in populations how are allele and genotype frequencies calculated using the hardy-weinberg equations what do changes in allele frequencies provide evidence for and then finally what are the impacts on the population if any of the conditions of hardy weinberg are not met so hardy-weinberg is a model for describing and predicting allele frequencies in a non-evolving population a population in hardy-weinberg equilibrium is not evolving frequencies of alleles in genotypes stay the same generation after generation for a population in hardy-weinberg equilibrium five conditions that must be met for a population to be in hardy-weinberg equilibrium include one a large population meaning no genetic drift two an absence of migration so no gene flow three no net mutations so no genes are modified deleted or duplicated four random mating so no sexual selection and then finally an absence of selection so no natural selection these conditions are rarely met but they provide a valuable null hypothesis allele frequencies in a population can be calculated from genotype frequencies using the hardy-weinberg equations p squared plus 2pq plus q squared equals 1 is one of those equations where p squared is equal to the frequency of the homozygous dominant genotype 2pq is equal to the frequency of the heterozygous genotype and q squared is equal to the frequency of the homozygous recessive genotype remember this is used to determine genotype and or phenotype frequencies of individuals in a population p plus q equals one is where p is equal to the frequency of the dominant allele and q is equal to the frequency of the recessive allele this is used to determine the frequency of a particular allele in a population now changes in allele frequencies provide evidence for the occurrence of evolution in a population these factors can disrupt hardy-weinberg equilibrium and change allele frequencies within a population one of these doctors mutations changes in genes can occur through random events that delete insert or substitute nucleotides another factor non-random mating individuals choose to make with another based on certain traits gene flow is another factor where new genes can be introduced to populations so migration of individuals in and or out of a population drift is where changes in the allele frequency within a population can occur due to random environmental events think bottleneck founder effects and finally natural selection alleles improve or reduce fitness for individuals to survive and reproduce in a given environment so let's look at an example we're going to look at a population of beetles in hardy-weinberg equilibrium the population consists of black and red beetles the dominant allele is black and we'll use capital a for that allele and the recessive allele is red and we'll use lowercase the black beetle population consists of the homozygous dominant and heterozygous genotypes and the red beetle population consists of the homozygous recessive genotypes for this population the dominant allele p is equal to 0.3 and the recessive allele q is equal to 0.7 with p plus q equals 1 so 0.3 plus 0.7 is equal to 1. now we're going to look at what is the frequency of the homozygous dominant genotype well we're going to use the equation p squared plus 2pq plus q squared equals 1. p squared is the frequency of the homozygous dominant genotype so p squared is equal to 0.3 squared equaling 0.09 or 9 for the heterozygous genotype it is equal to 2 pq which is equal to 2 times 0.3 times 0.7 which equals 0.42 or 42 and then finally what is the homozygous recessive genotype well that is equal to q squared which is 0.7 squared equaling 0.49 or 49 it is important to be mindful of your decimals when you're working with the hardy-weinberg equation so now let's look at an example that you're going to work through for this problem i would like you to pause your video solve the problem and then push play when you're ready with your answers welcome back for this question you were looking at what is the frequency of each genotype in this population and what is the frequency of the dominant phenotype the frequency of the homozygous dominant genotype is 0.36 the frequency of the heterozygous is 0.48 and the frequency of the homozygous recessive is 0.16 now what is the frequency of the dominant phenotype well that is going to be equal to both p squared and 2pq because both of them are going to exhibit the dominant phenotype and the answer there would have been .84 so now we're going to practice some more for this practice you're going to perform a mathematical calculation including mathematical equations in the curriculum so for this practice problem i would like you to hit pause read the question formulate your answer and then hit play again welcome back for this question you were supposed to look at based on the information provided which of the following best represents the calculated differences between the isolated population and the general population your answer should have been d that at the frequency of the ellis fan crevel allele is .0447 in the isolated population and .0026 in the general population which suggests that genetic drift has occurred in the isolated population a couple key points on solving this question is is that q squared was given to you where in the general population it was one in 150 000 live births and then in the isolated population it was 1 in 500 and the genetic drift occurred due to those isolated populations so what should you take away from this lesson today first hardy weinberg is a model for describing and predicting allele frequencies in a non-evolving population two the conditions for a population to be in hardy-weinberg equilibrium are a large population size absence of migration no net mutations random mating and absence of selection the allele in genotype frequencies can be calculated using the hardy-weinberg equation where p and q represents alleles and p squared 2pq and q square represent the genotypes changes in allele frequencies provide evidence for the occurrence of evolution in a population and then finally a population can evolve if the conditions of hardy-weinberg are not met with small populations being more susceptible to random environmental impacts than large populations well i hope this video has been helpful until next time thank you