Hardy weinberg equilibrium

hardy weinberg

1. Welcome P.TEJASREE BAM-20-27 Dept Of GPBR

2. Hardy Wienberg Equilibrium

3. Learning Objectives what is population What is population genetics What is Mendelian population What is gene pool What is gene frequency What is genotypic frequency What is Hardy-Weinberg Equilibrium What are evolutionary forces in a population What are the significance of Hardy-Wienberg equilibrium Factors affecting H-W principle

4. What is a Population Definition : A group of individuals of a particular species occupying a definite space, in which the individuals interact, interbreed and exchange genetic materials. Species is a group of living organism comprising of similar individuals capable of exchanging genes through interbreeding Individuals of same species of a particular region is called population A part from its ecological significance, population has a important role in the process of evolution

5. What is Population genetics Study of distributions and changes of allele frequency and interaction of allele in a population Population is prone to the four main evolutionary forces: 1. Natural selection 2. Genetic drift 3. Mutation 4. Migration Study of population genetics is essential for species adaptation and evolution

6. For better understanding of population genetics we must study 1.Mendalian population 2.Gene pool 3.Gene frequency 4.Genotypic frequency 5.Hardy Weinberg Law 6.Evolutionary forces in population

7. Mendelian Population A group of sexually interbreeding organism also called as genetic population or random mating population Definition: A community of similar individuals living within a circumscribed area at a given time and capable of interbreeding to produce fertile offspring's. Mendelian population is characterized by individuals having somewhat similar genetic constitution

8. Gene pool Sum total of genes present in the Reproductive individuals of a population called Gene pool A gene pool of population describes: 1. Gene present in the population 2. Properties different kinds of gene 3. Pattern of distribution of gene in the individuals of population

9. Allelic frequency Suppose there are 100 individuals in a population, in which 40 are homozygous dominant (AA) 40 are heterozygous dominant(Aa) 20 are homozygous recessive(aa) The frequency of ‘A’ allele will be (p) (119+1/2 *76)/208=0.75 The frequency of ‘a’ allele will be (q) (13+1/2*76)/208=0.25 Gene frequency calculated by dividing the no.of a particular allele with total no.of allele present on that locus in the population

10. GENOTYPE FREQUENCY Definition: The Proportions of different genotypes for a gene in a population are known as genotypic frequency Genotype frequency is the proportion of a genotype in a sample will be the ratio of the number of individuals having that genotype to the total number of individuals in the sample. Genotypic frequencies for MN blood group L^M L^M = 0.57 (119/208) p2=0.56 L^M L^N = 0.36 (76/208) 2pq = 0.38 L^N L^N = 0.06 (13/208) q2=0.06

11. Gene frequency Definition : Proportion of different alleles of a gene present in a Mendelian Population are known as Gene frequency If a gene has two alleles for eg ; L^M And L^N, their frequencies may be represented by p and q p = 0.75 , q = 0.25 p+q = (0.75+0.25) p+q = 1 p = 1-q ,q = 1-p For gene with multiple alleles The A-B-O blood types are determined by three alleles I A ,I B ,and i Frequencies of these are p,q and r respectively The frequencies of 6 different genotypes in the A-B-O blood typing system are obtained by expanding the trinomial ( p+q+r ) 2 =p 2 +q 2 +r 2 +2pq+2qr+2pr

12. N :- Total no.of individuals in the population D :- Total no.of homozygous dominant H :- Total no.of heterozygous dominant R :- Total no.of homozygous recessive Genotypic frequency of AA individuals D/N G.f of Aa individuals H/N G.f of aa individuals R/N

13. HARDY WIENBERG’S EQUILIBRIUM Hardy – Wienberg law is the fundamental law of population genetics This law was developed independently by Hardy (1908) in england and Weinberg (1909) in germany The Hardy-Weinberg law States that gene and genotype frequencies in a mendelian population remain constant generation after generation if there is no selection , mutation , or random drift. Hardy & Wienberg

14. H-W law describes a theoretic situation in which a population is undergoing NO evolutionary changes. It explains that: The evolutionary forces are absent The population is large Its individuals have random mating Each parent produce roughly equal number of gametes The gametes produce by the mates combine at random and the gene frequency remain constant The genetic equilibrium of the gene is maintained and the variability present in the population is preserved

15. Significance Gene and genotype frequencies of different allele of a gene in a population remain equilibrium Mating is completely random phenomenon in a population Only large population follow H-W law of equilibrium Gene frequencies will be unpredictable in small population All the genotypes in a population reproduce equally successfully The variation in H-W equilibrium is produced by mutation , selection , and genetic drift these are the evolutionary forces in a population If these evolutionary forces not there in the population, it follows H-W equilibrium A population in H-W equilibrium do not show evolution

16. Evolutionary Factors Affecting MUTATIONS: - p = v / u+v , q = u / u+v Mutation in only one direction can cause one allele slowly to replace another. Mutation in both directions results in an equilibrium with frequencies determined by the mutation rates. Mutation may produce new allele or may change the frequency of existing allele which is not in that population. MIGRATION : Ne=4N*Nm / ( Nf+Nm ) , m = M / N+M Migration between population always causes the gene frequencies of the receiving population to shift towards those of the immigrants This addition or removal of alleles when individuals enter or leave a population from another locality is called gene flow Wright estimated small amount of migration m=0.0001

17. NON RANDOM MATING INBREEDING : results in more homozygotes ASSORTATIVE MATING : mating according to phenotype , mating between phenotypically similar individuals being either more frequent or less frequent NATURAL SELECTION: Fitness (W)= R i / R h If selection occurs in such a way that out of the 2 alleles only 1 allele is preferred by nature . It leads to change in the equilibrium . The genotype having fitness of 1 are favoured by selection , the magnitude of selection aganist a genotype is called selection coefficient or selection differential . RANDOM GENETIC DRIFT : Random change in gene frequency or allele frequency due to sampling error . It occurs in small populations becoz of greater sampling error . Sampling errors lead to – Fixation of certain alleles Elimination of some other alleles

18. Gametic selection : when selection acts on gametes or on the haploid phase of life cycle is called gametic selection . Ex :- fungi Thus in each generation , the frequency of a allele will decline by the proportion s till it reaches zero , and A becomes fixed in the population . Zygotic selection :- selection operates on the zygotes or the diploid phase is called zygotic selection . Zygotic selection may be :- aganist the recessive phenotype Aganist the dominant phenotype In the favour of heterozygote FOUNDER PRINCIPLE :- the genetic divergence created by the limited no.of founders of new populations is called the founder principle . Ex :- Evolution of Darwin finches on Galapagos Islands which were probably derived from a few initial founders A new population of a species is often initiated by a relatively small no.of individuals of a population ; these individuals are called founders of the new population .

19. Reference GENETICS – P.S VERMA GENETICS –B.D.SINGH

20. Thank You Submitted to :- Dr Lal Ahamad Associate Professor Dept of GPBR