Population Genetics :
A group of inbreeding individuals can constitute population. Population genetics deals with the frequencies of different alleles in different groups of population and reveal the mechanism causing genetic diversity between them.
Hardy – Weinberg Law :
It states that gene frequencies of various genes in a large, random matting population remain constant generation after generation in absense of mutation, selection and migration.
Derivation :
Assumes that there are ‘N’ number of individuals where the genes are biallelic containing alles B1 and B2 with frequency p and q respectively.
‘p’ is the frequency of B1 allele
‘q’ is the frequency of B2 allele
‘N’ is the total number of individuals and
So that, ( p+q = 1) or p = ( 1-q ) or q = ( 1- p )
The population can have three types of genotypes viz ; B1B1, B1B2 and B2B2 and let the frequency can be P, H and Q respectively.
Gene ( alleles)
B1 B2
Genotypes
B1B1 B1B2 B2B2
Frequency – p of B1 and q of B2
– P of B1B1, H of B1B2 and Q of B2B2
If there are ‘N’ number of individuals in the sample, there will be
P individuals with genotype B1B1
H individuals with genotype B1B2
Q individuals with genotype B2B2
So that ( P+H+Q ) = N
By the given genotypes we can calculate the allelic frequencies i.e. frequency of’p’and’q’by gene counting method.
The allele frequency of ‘p’ = ( P + 1/2 × H ) × 1/N
=B1B1/N + 1/2 × B1B2/N
The allele frequency of ‘q’ = ( Q + 1/2 × H ) × 1/N
=B2B2/N + 1/2 × B1B2/N
The frequency of’p’and’q’also can be termed as number of gametes in population, because we know that gamete always contain a single allele.
In random matting as per Hardy – Weinberg law the random union of types of gametes produced from parents occurs which can be written by simple multiplication of gametic types produced by the parents.
| Male Gamete | Male Gamete | ||
| B1 | B2 | ||
| Female Gamete | B1 | B1B1 | B1B2 |
| Female Gamete | B2 | B2B1 | B2B2 |
∴ Genotypes = B1B1 : 2B1B2 : B2B2
Frequency ; p2 of B1B1, 2pq of 2B1B2 and q2 of B2B2
Allele B1 and B2
Absolute Frequency ; P, H and Q
Application of law to human population :
i ) Broadly the Hardy-Weinberg Equilibrium ( HWE ) principle helps to find out the gene frequencies of a random matting population which are generally influenced by demographic factors, population structure, and evolutionary factors like selection and mutation.
Some important application of HWE are as follows ;
i) HWE has helped us to find out the number of alleles present in ABO locus and thier frequency at particular locus.
ii) HWE is helped in finding out the nature of HbS allele and it’s equilibrium.
iii) HWE is helps us to understand some health problem in small isolated population.
iv) In forensic application HWE helps in solving the problems related to paternity disputes by analysing the inheritance pattern.
v) It also helps in understanding the genetic disorders which may be influenced by environment in some extent and in order to calculate the impact of genetic and environment the HWE principle has a great role.
vi) It helps in calculates genetic diversity, the demographic effects upon gene frequency and origin of new variants of allele etc.