0:00:00.000,0:00:06.000 Hello everyone, I welcome you to another lecture from the Animal Genetics module, 0:00:06.000,0:00:12.000 the topic of which is Genetic variability in populations and Hardy-Weinberg equilibrium. 0:00:12.000,0:00:21.000 In the lecture, we will introduce the background of genetic variability and the already mentioned Hardy-Weinberg equilibrium. 0:00:21.000,0:00:29.000 We understand genetic variability as the representation of individual genotypes and genes (alleles) 0:00:29.000,0:00:34.000 in the population and their changes in the sequence of generations. 0:00:34.000,0:00:42.000 The basis of genetic variability is the representation of individual genes at the individual level. 0:00:42.000,0:00:50.000 We can imagine genetic variability at the individual level using the following example. 0:00:50.000,0:00:57.000 Consider that individual phenotypes in a population are based on a gene series. 0:00:57.000,0:01:06.000 It means that a more significant number of alleles, in our case four, will occur in the population for the given trait. 0:01:06.000,0:01:15.000 Individual alleles are located on one locus and show complete dominance among themselves. 0:01:15.000,0:01:21.000 In our case, the wild allele is completely dominant over all other alleles, 0:01:21.000,0:01:27.000 and the allele for albinotic colouring is recessive for all other alleles. 0:01:27.000,0:01:33.000 Since the genotype for a given trait consists of only two alleles, 0:01:33.000,0:01:40.000 an individual can exhibit only one of four phenotypic colours. 0:01:40.000,0:01:49.000 From the point of view of genetics, we are mainly interested in the genetic variability within the population, 0:01:49.000,0:01:56.000 which is based precisely on the individual's genetic variability. 0:01:56.000,0:02:05.000 Genetic variability at the population level monitors the population's representation of individual genotypes 0:02:05.000,0:02:09.000 and genes and its changes between subsequent generations. 0:02:09.000,0:02:17.000 For example, let's assume a population of 10 individuals with the indicated phenotypes: 0:02:17.000,0:02:22.000 5 wild colourd, three chinchillas and two Himalayan. 0:02:22.000,0:02:32.000 Since each individual carries two alleles for a given colour, there are 20 alleles in a given population (generation). 0:02:32.000,0:02:37.000 We will further predict the following representation of alleles. 0:02:37.000,0:02:44.000 It means that in a given generation (population) there are seven alleles for wild colour, 0:02:44.000,0:02:53.000 five alleles for chinchilla colour, four alleles for Himalayan colour and four alleles for albino colour. 0:02:53.000,0:03:00.000 We can find the proportion of single alleles shown here based on the individual ratios. 0:03:00.000,0:03:12.000 Furthermore, we were to consider that we are only interested in the frequency of the allele for wild colouring and the alleles of the others. 0:03:12.000,0:03:30.000 In that case, that means the sum of all other alleles, we get an allele frequency of 0.35 for the allele for wild colouring and 0.65 for the other forms of colours. 0:03:30.000,0:03:37.000 Populations can be divided into populations with multiallelic polymorphic loci, 0:03:37.000,0:03:48.000 meaning there are different genotypes in the population, and more forms of alleles of one gene are represented. 0:03:48.000,0:03:59.000 Furthermore, the population with monomorous loci means that there is only one type of allele in the population, 0:03:59.000,0:04:12.000 and the population with polymorous loci are byallelic, which means that only two forms of alleles of one gene occur in the population. 0:04:12.000,0:04:17.000 If we consider a population with biallelic loci and incomplete dominance, 0:04:17.000,0:04:24.000 three different of phenotypes based on three different of genotypes will occur in the population. 0:04:24.000,0:04:31.000 Dominant homozygotes, heterozygotes and recessive homozygotes. 0:04:31.000,0:04:36.000 We denote the absolute number of dominant homozygotes as capital D, 0:04:36.000,0:04:46.000 the absolute number of heterozygotes as capital H and the absolute number of recessive homozygotes as capital R. 0:04:46.000,0:04:52.000 The total number of individuals in the population is denoted as capital N. 0:04:52.000,0:05:01.000 The frequencies of individual genotypes are obtained as the ratio of individual of absolute numbers of genotypes 0:05:01.000,0:05:05.000 to the total number of individuals in the population or generation. 0:05:05.000,0:05:11.000 We mark the relative number of dominant homozygotes with a small "d", 0:05:11.000,0:05:20.000 the relative number of homozygotes with a small "h" and the relative number of recessive homozygotes with a small "r". 0:05:20.000,0:05:30.000 Based on the relative frequencies of every genotypes, we are also able to determine the relative number of alleles in the population. 0:05:30.000,0:05:41.000 When we denote the relative number of dominant alleles as a small "p" and get it as the sum of the relative frequencies of dominant homozygotes 0:05:41.000,0:05:45.000 and half the relative frequency of heterozygotes. 0:05:45.000,0:05:55.000 Since a dominant homozygote carries both dominant alleles and a heterozygote only one dominant allele, 0:05:55.000,0:06:02.000 this means half of its genotype, therefore only half the frequency of heterozygotes. 0:06:02.000,0:06:08.000 We mark the relative frequency of the recessive allele in the population with a small "q". 0:06:08.000,0:06:16.000 The equivalence relation can be used to obtain the relative frequency of the recessive allele, 0:06:16.000,0:06:26.000 where it is the sum of the relative frequency of recessive homozygotes and half the relative frequency of heterozygotes. 0:06:26.000,0:06:35.000 If we know the frequencies of individual alleles participating in maating procesreproduction, 0:06:35.000,0:06:41.000 we can estimate the relative genotypic representation of the next population. 0:06:41.000,0:06:49.000 A homozygous dominance in the next generation will result from the combination of the dominant allele from the sire 0:06:49.000,0:07:02.000 and the dominant allele from the dam, that is, the frequency of the dominant allele in the subpopulation of male and the frequency of the dominant allele in the subpopulation of females. 0:07:02.000,0:07:10.000 Since we expect that the frequencies of dominant alleles in the subpopulation of male and female are the same, 0:07:10.000,0:07:21.000 and mathematically, these frequencies are multiplied, it follows that the frequency of dominant homozygotes in the next generation, 0:07:21.000,0:07:26.000 we get the as square of frequency of dominant alleles. 0:07:26.000,0:07:34.000 We proceed similarly with the frequency of recessive homozygotes in the next generation, 0:07:34.000,0:07:45.000 when we obtain as square of the frequency of recessive alleles. The genotype of the heterozygote in the next generation can be obtained in two ways. 0:07:45.000,0:07:56.000 The first way is when the dominant allele is passed on by the sire and the recessive allele by the dam, 0:07:56.000,0:08:03.000 or vice versa; the individual gets the recessive allele from the sire, and the dominant allele gets it from the dam. 0:08:03.000,0:08:20.000 Therefore the expected frequency of heterozygotes in the next generation can be optain as twice the frequency of dominant alelles times frequency of recessive alleles in the parent population. 0:08:20.000,0:08:34.000 Generally, the markings, small “d”, small “h”, and small “r”, are given as the frequency of genotypes in the base populations 0:08:34.000,0:08:44.000 and p2, 2pq and q2 as the frequency of genotypes in the next generations. 0:08:44.000,0:08:50.000 Another concept that we will deal with in the lecture is the Hardy-Weinberg equilibrium. 0:08:50.000,0:09:04.000 The principle of Hardy-Weinberg equilibrium is that the frequency of alleles and genotypes in a population remains constant, i.e. unchanged. 0:09:04.000,0:09:09.000 If we talk about the population as being in the Hardy-Weinberg equilibrium, 0:09:09.000,0:09:15.000 the frequency of genotypes and genes remains constant from generation to generation. 0:09:15.000,0:09:20.000 It is true if there are no interfering howls. 0:09:20.000,0:09:31.000 In to interfering howls we can include Selection, Mutation, Migration, Non-Random Maiting and Genetic Drift. 0:09:31.000,0:09:36.000 It is important to realize that outside of laboratory conditions, 0:09:36.000,0:09:44.000 at least one or more of these "interfering" influences are always present. 0:09:44.000,0:09:58.000 Hardy-Weinberg equilibrium is impossible. Genetic equilibrium is an ideal state that provides a basis for measuring genetic change in a population. 0:09:58.000,0:10:06.000 Examples of how the mentioned phenomena disrupt the Hardy-Weinberg equilibrium are given in the following pictures. 0:10:06.000,0:10:14.000 If we select only a specific genotype from the base population as the parent of the next population, 0:10:14.000,0:10:18.000 we will change the genetic background in the next population. 0:10:18.000,0:10:26.000 Similarly, the mutation also changes the genetic beckground of the population because 0:10:26.000,0:10:32.000 if one allele for wild colour is mutated to an allele for chinchilla colour, 0:10:32.000,0:10:41.000 or a mutation occurs from an allele for colour of a Himalayan colour to an allele for chinchilla colour, 0:10:41.000,0:10:47.000 again, there will be a change in the frequencies of genotypes in the population. 0:10:47.000,0:10:58.000 During the immigration of genotypes from foreign populations or the emigration of genotypes to other populations, 0:10:58.000,0:11:06.000 there must again be a change in the ratio of genotypes in the population of individuals. 0:11:06.000,0:11:19.000 We can take non-random mating as equivalent to selection and, therefore, also change the representation of genotypes in the next population. 0:11:19.000,0:11:31.000 Another phenomenon that disrupts the Hardy-Weinberg equilibrium is genetic drift. 0:11:31.000,0:11:40.000 It is generally assumed that if a population is in Hardy-Weinberg equilibrium, it is in infinite size. 0:11:40.000,0:11:46.000 However, this fact does not apply to the general population. 0:11:46.000,0:11:56.000 If we have two populations with the same frequency of individual genotypes, the given populations differ in absolute size. 0:11:56.000,0:12:12.000 Thus, even with the exclusion of other disturbing phenomena in the subsequent generation, other characteristics of the genotypes can be expected. 0:12:12.000,0:12:23.000 Because in smaller populations the rule that each individual has the same probability of becoming the parent of individuals 0:12:23.000,0:12:27.000 in the subsequent population is violated. 0:12:27.000,0:12:39.000 Let's again consider a population with biallelic loci and incomplete dominance and consider that the population is in Hardy-Weinberg equilibrium 0:12:39.000,0:12:49.000 so that no disturbing phenomena such as selection, mutation, migration, genetic drift or non-random mating will be present. 0:12:49.000,0:12:57.000 The number of alleles and individual genotypes will be constant, meaning that in any next generation, 0:12:57.000,0:13:06.000 the relative frequency of individual genotypes will be the same as the relative frequency in the starting population. 0:13:06.000,0:13:14.000 It follows from the nature of the Hardy-Weinberg equilibrium that the highest frequency of heterozygotes in the population, 0:13:14.000,0:13:20.000 when the Hardy-Wienberg equilibrium is maintained, is equal to 50%. Therefore, 0:13:20.000,0:13:26.000 if a population's relative frequency of heterozygotes is higher than 50%, 0:13:26.000,0:13:30.000 the given population cannot be in Hardy-Weinberg equilibrium. 0:13:30.000,0:13:38.000 In this lecture, we introduced the basic of genetic variability and the principles of Hardy-Weinberg equilibrium. 0:13:38.000,0:13:44.000 Thank you for your attention, and I look forward to meeting you at the following lecture.