This document provides an overview of the Hardy-Weinberg law in population genetics. It defines the Hardy-Weinberg principle as stating that allele and genotype frequencies will remain constant from one generation to the next in a population where no evolutionary influences are present. The history of the law developed from the work of Hardy in 1908 and Weinberg in 1908 is discussed. The key assumptions required for Hardy-Weinberg equilibrium - including random mating, large population size, no natural selection or gene flow - are outlined. Equations for calculating expected genotype frequencies based on allele frequencies are presented along with an example calculation.

1. HARDY – WEINBERG LAW
Submitted to –Dr. Sapna Sharma mam
Submitted by – Shabnam
Roll no. – 1303
Class – Msc forensic science 2nd 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.

6. 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 p2 , 2pq and q2.
 This frequency distribution will not change from
generation to generation once in Hardy-Weinberg
equilibrium.

7. BASIC CONCEPTS
 Genome-Complete set of DNA, including all of it’s
genes(of organism).In human being ,copy of entire
genome more than 3billion 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.

8. 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.

9. 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=p2
the frequency of genotype Aa=2pq
the frequency of genotype aa= q2
mathematical, p+q=1
p2 + 2pq + q2 = 1

11. PUNNETT SEQUARE
 Heterozygous male- Aa
 Heterozygous Female- Aa

12. 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.

17. 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.

18. HARDY - WEINBERG ASSUMPTIONS
 The final conclusions of Hardy-Weinberg
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

19. RANDOM MATING
 Organisms mate randomly with 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.

21. 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.

23. 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.

24. 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.

25. 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.

28. 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.

29. FOUNDER EFFECT

30. 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.

32. 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.

33. 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.

34. 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.

35. 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.

36. CHROMOSOME MUTATIONS
 May involve changing the
structure of a chromosome.
 May include the loss or gain of a
part of chromosome.

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

38. THANKYOU