In the year 1908,
British mathematician Godfrey H. Hardy and German physician Wilhelm Weinberg were
said to have discovered the relationship between gene and genotype frequencies,
generally known as the Hardy-Weinberg principle, or the Hardy-Weinberg equilibrium
(Chen, 2010). Since when it has been discovered, the Hardy-Weinberg principle
has become a powerful research tool in both theoretical and applied research in
population and quantitative genetics (Chen, 2010).
Hardy-Weinberg principle states that; under the condition of a large
population size, diploid organisms with non-overlapping generations and random
mating, the genotype frequencies at a locus are determined by the allele
frequencies, and both the genotype and the allele frequencies will stay constant
in future generations when there is no condition of mutation, migration and selection.
(evolutionary forces). (Chen, 2010).
A tool in
population genetics that has been generally used to detect potential or
possible typing error is testing for Hardy-Weinberg equilibrium. It is also
much used to check both single nucleotide polymorphism (SNP) and microsatellite
genotype data (Chen, 2010). Hardy-Weinberg equilibrium is not very sensitive to
certain kinds of deviations from these theories and the effects of the
deviations from several theories can cancel the effects of each other out. So Therefore,
due to the ensuing consequences, violation from these theories may not
necessarily result in an observable deviation from Hardy-Weinberg proportions.
But deviation from the Hardy-Weinberg equilibrium itself strongly suggests that
at least one of the assumptions/theories is violated. There are many
possible reasons for a significant deviation from Hardy-Weinberg equilibrium.
For instance, population stratification could result in non-random mating.
Alternatively, the researcher might have not correctly specified the underlying
genetic basis for the trait of interest. The realization of significant
deviation from Hardy-Weinberg equilibrium can potentially lead to a better
genetic model and establishing interesting alternative hypotheses for further
investigation. Because of its elegance and theoretical importance, the
Hardy-Weinberg principle has become an important starting point for population
genetic investigations. (Chen, 2010)
HARDY-WEINBERG LAW AND ESTIMATING ALLELE FREQUENCE
the keystone of population genetics is the Hardy-Weinberg
law or principle.
The law consists of two parts. They are as follows:
first part; states that in a large, randomly mating population with two alleles
at a locus (e.g B & b), there is a simple relationship between these
allele frequencies (frequency of B = p; frequency of b = q)
and the genotype frequencies (p2, 2pq, or q2) which they define.
second part; holds that this relationship between allele and genotype
frequencies (as I earlier explained), based on the binomial expansion of (p + q)2, do not change from one generation to the next.
a population follow these two parts of the law, it is in Hardy-Weinberg
equilibrium. In populations like that, the law is of major importance
in showing why the frequency of dominant traits do not increase from one
generation to the next and why recessive traits do not decrease. Furthermore,
the law is consistently used in when doing genetic counselling where estimates
of genotype, allele, and carrier frequencies are calculated from limited
in small families, with such estimates then being employed to estimate specific
genetic risk (Chen, 2010)). The study of deviation from
Hardy-Weinberg equilibrium using an Expectation-Maximization (EM) statistical
algorithm, is being used in the investigation of allelic frequency estimation (Chen,
IMPORTANCE OF HARDY-WEINBERG
hardy-Weinberg principle as we have explained before is very Important in
population genetics, among the importance is the fact that, due to the fact
that there are many assumptions needed to derive the Hardy–Weinberg Law, we learned
that it plays a central role in the theory of population genetics. That
is due to two reasons;
First of all; it is very
important due to the fact that it provides a route for researchers to estimate the
frequencies of alleles for a particular characteristic in which what we call heterozygotes
cannot be distinguished from the homozygotes, given the fact that we are
willing to assume that all of the assumptions apply to the population in which
we are working on.
Secondly; using the
knowledge of hardy-weinberg principle, we know what will happen in a population
when there is no presence of any evolutionary force (e.g., mutation, selection,
adaptation etc.). referring to this, the known philosopher Elliott Sober, made
an important quote, “it plays an important role in the study of population genetic theory similar to the role
that we know that is performed by the first and second laws of motion play in
what is known as Newtonian mechanics” (Holsinger, 2001)
order for us to explain the words of the philosopher Elliott Sober, we explain
the first and second laws of newton and how we can compare it to the hardy
Weinberg principle for better explanation;
The first laws of motion which is also the law
inertia states that an object at rest will remain at rest and an object in
motion will remain in motion (in a straight line at a constant speed and
direction) unless if it is acted on by external forces. They are what can be termed as ‘zero-force laws’ because
they answer the question of what we should expect when no evolutionary forces (e.g., mutation, selection, adaptation etc.) act on an object.
Moreover, the 2nd law of motion give us the ability to judge
the magnitude and direction of any force operating on an object by the
acceleration to which it is subjected to. (Holsinger, 2001)
So, since we compared
the Hardy-Weinberg law to the first two laws of newton and we called the two
laws of newton zero-force laws, The Hardy–Weinberg law is what is known
as population genetics’ zero-force law. It makes us know how a
population will look like if a phenomenon such neither genetic drift (random
species movements) nor any evolutionary force (e.g.,
mutation, selection, adaptation etc.) affect it.