Hardy – weinberg law

Forensic science

1. Hardy – weinberg law Submitted to –Dr. Sapna S harma mam Submitted by – Shabnam Roll no. – 1303 Class – Msc forensic science 2 nd year

2. Contents 1. DEFINITION 2. HISTORY 3. HARDY-WEINBERG EQUILIBRIUM 4. HARDY-WEINBERG EQUATIONS 5. CALCULATIONS FROM HARDY- WEINBERG EQUATION. 6 . HARDY-WEINBERG ASSUMPTIONS.

3. Definition In population genetics , the Hardy – Weinberg principle,law,equilibrium or theorem states that allele and genotype frequencies in population will remain constant from generation to generation in absence of other evolutionary influences.

4. History As we known about Mendelian genetics ,even after many geneticists had accepted Mendel’s law , confusion lingered regarding the maintenance of genetic variation in natural populations. Some opponents of the Mendelian view contended that dominant traits should increase and decrease in frequency, which is not observed in real populations. Hardy (1908) refuted such arguments in paper that,along with an independently published paper by Weinberg (1908) laid down the foundation for the field of population genetics.

5. Hardy-Weinberg equilibrium The Hardy-Weinberg law/theorem deals with Mendelian genetics in the context of populations of diploid, sexually reproducing individuals. Given set of assumptions this theorem states that: 1. Allele frequencies in population will not change from generation to generation. 2. If the allele frequencies in a population with two alleles at a locus are “p” and “q”, then the expected genotype frequencies are p 2 , 2pq and q 2 . This frequency distribution will not change from generation to generation once in Hardy-Weinberg equilibrium.

6. Basic concepts Genome -Complete set of DNA, including all of it’s genes(of organism ).In human being ,copy of entire genome more than 3 billion DNA base pairs in all cells that have nucleus. Gene frequency- Relative proportion of a particular genes or alleles of single locus in a population. When be consider a particular gene on single locus in population , then we note the probability of a particular genes.One character dominant in a population while other is reccessive .

7. CONTS. Genotypic Frequency -Relative proportion of a particular genotype in population. Population Genetics -Study of allele frequency and genotype frequency . Population -It is freely interbreeding group of individuals. Allele frequency- It is number of individuals alleles of certain type divided by total number of alleles of all types in a population. Gene locus- It is the portion on chromosome that representing single gene.

8. Hardy-Weinberg equation For example - If the frequency of allele ‘A’ in the population is ‘p’ and the frequency of allele “a” in the population is “q”. Then the frequency of genotype AA=p 2 the frequency of genotype Aa =2pq the frequency of genotype aa = q 2 mathematical, p+q =1 p 2 + 2pq + q 2 = 1

9. Punnett sequare Heterozygous male- Aa Heterozygous Female- Aa

10. Calculations by Hardy-Weinberg law Ques. In population of cats can either black or white : the Black allele (B) has completely dominance over the white allele (b). Given population of 1000 cats , 840 black cats and 160 white cats. Determine the :- a) Allele frequency of individuals per genotype. b) Number of individuals per genotype.

11. Hardy-Weinberg proportions Hardy-Weinberg theorem demonstrates that Mendelian loci segregating for multiple alleles in diploid populations will retain predictable levels of genetic variation in absence of forces that change allele frequencies.

12. Hardy - Weinberg assumptions The final conclusions of Hardy- W einberg theorem apply on the basis of following assumptions : 1. Random mating 2. Very large population 3. Absence of natural selection 4. No gene flow or migration 5. No mutation

13. Random mating Organisms mate randomly w ith each other, no preference with a particular genotypes. This type of mating leads to the resultant production of the same number of offspring for all females in a population which tends to maintain genetic equilibrium. Hence, to attain the genetic equilibrium ,random mating should occurring in the population.

14. Non - random mating Non-random mating is, mate with selective partner which is responsible for causing change in genetic equilibrium because there is no gene flow in a whole population .

15. Infinite large population To maintain the genetic equilibrium the population should be effectively infinitely large in size. Because of that genetic drift is not causing a random changes in allele frequencies due to sampling error from one generation to the next generation. Genetic drift :- Genetic drift is a change in the frequency of an allele within a population over time. This change in frequency of the allele or gene variation must occur randomly in order for genetic drift to occur.

16. Genetic drift Genetic drift describes random fluctuations in the numbers of gene variations in population , gene also called allele increases or decreases by chance over time. These variations in the presence of alleles measured as changes in the allele frequencies. All natural populations are finite and thus subjected to drift, but we expect the effects of drift to be more pronounced in small than in large populations.

17. Factor promote the genetic drift Two type of events promote genetic drift :- Bottleneck effect :- Bottle neck can change the proportional random distribution of alleles and ever leads to loss of alleles. The chance of inbreeding and genetic homogeneity can increase.Smaller population size can also cause deleterious mutations to accumulate. Example:- Seal population of northern californian sea in 1890 .

18. Founder effect It is the loss of genetic variation that occurs when a new population is established by a very small number of individual from a larger population. It also leads to change occur in the equilibrium population because it is continuity of process which tends to change the population. Example:-South Africa human population they was founding with dutch people at starting found with 20 dutch people, they many of them demarks Huntington’s disease in those dutch people after a time period rate of huntington’s disease is very high in South Africans population.

19. Founder effect

20. Natural selection Is the differential survival and reproduction of individuals due to difference in the phenotype. It is a key mechanism of evolution,the change in the heritable traits characteristics of the population over the generation. Hence , to apply the Hardy-Weinberg law the natural selection should be absent.

21. No gene flow / migration Migration is the movement of an organisms from one place to another with intent to settle. Causes of migration due to environmental conditions/factors such as need for resources due to over population were often cause of migration. Immigration:- Coming into the particular groups/population from other area. Emigration :- Leaving habitat area to move to another area.

22. Conts . Migration is ultimately leads to genes disturbs in the population. It is responsible for adding and deleting the alleles from the population. Due to gene flow, population becomes unstable and disturbs the genetic equilibrium. Hence, migration should not be present in the population to attains the Hardy-Weinberg equilibrium.

23. Mutations Mutation is the alteration in the nucleotide sequence in the genome of an organism , virus or extra-chromosomal DNA. Mutation is the ultimate source of genetic variation, preventing populations from becoming genetically homogeneous in situations where they otherwise would.

24. Spontaneous mutation Spontaneous mutation is the result of errors in the natural biological processes.The induced mutations are due to agents in the environment that causes change in DNA structure. Spontaneous mutations are alleles of initially unknown gene. Occur naturally but change in DNA sequence during replication.

25. Chromosome mutations May involve changing the structure of a chromosome. May include the loss or gain of a part of chromosome.

26. Referances www.nature.scitable hardy weinberg law www.youtube.com Shomu’s biology www.wikipedia.com https://www.scienceDirect.com www.germanna.edu.com

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