1. Changes of gene frequency and its agencies
Definition
Gene frequency means frequency for a gene which means in how many times a particular
allele or a version of allele is repeating in particular locus of a whole population.
It helps to understand genetic diversity of a population.
Let us take an example we will find gene A in whole population having fixed locus .we will e
finding all the gene at same locus let say locus is L and we will find gene present at particular
locus we will finding all the locus with allele A .If we have 20 chromosome in a population
and we have 12 allele present within a population by formula we will get gene frequency
Formula : Gene frequency = No of copies of particular allele x100
Total number of all allele in a locus
12/20x100
Gene frequency for allele A= 60 percent
So it means that the frequency of that particular gene within a particular population is 60%
Changes of gene frequency
The following are the facotrs that cause changes in gene frequency
Mutation
Migration
Genetic drift
Non -Random mating
Selection
Inbreeding coffecient
Genetic drift :
Allele frequency can be changed over time so if a allele frequency of population is changed
due to effect of chance and randomness we call it genetic drift. According to hardy Weinberg
principle the allele frequency of a population should remain constant if there is not any
evolutionary influences over time like no immigration etc .Genetic drift occurs when the
population size is small as the size is small so allele will not follow hardy Weinberg
principle. Genetic drift occurs due to chance or randomness and size of population is small in
it.
Two types of genetic drift
Bottle neck effect
Founder effect
2. Bottle neck effect : When a population is squeezed through a bottle and its number decrease
rapidly. Like genetic drift takes place in a population which lose lot of change in allele so we
have a little change in a population
Example : Northern seals live in US in 1890s .In early time we had 100,000 number of
population . But after human interruption their number decreases and there was a time a time
when their number decreased to 50 population and population squeeze to bottle neck and
there is so many chance of genetic drift there. Which then rise to 150,000 when human
understand their importance .Now the population comes back to normal shape. But now the
population undergo small changes and is different from the population which was in 1890s.
Founder effect :
In it a population is founded in new locality and was not present there before. If that
population will not from interaction with already present species then the frequency of allele
will be changed as compared to parental population.
Migration
It menas that the individual move from one place to another and thus their alleles moves too
causing change in the gene frequency within population. It also cause change in gene
frequency which means that the organisms move inside and out of the population.
It is of two kinds
Emigiration.
Immigration
Emigiration if the individual moves outside of the population it is called emigiratio
Immigiration means the migration of species in a particular population .
These results in the flow of genes from one population to another. If the rate of gene flow or
allele frequency is more within a population then it will result in the ofrmation of single
effective population .
For a larger population the allele frequency will not be changed due to migration
If the population size is small , then there will be change in alllele frequency due to
migration.
Mutation
These are the disrupting influencers. It is important for organisms with short generation
time.It is one of the major source of change in gene frequency. There are two kinds of
mutation forward and reverse mutation .like if we have two dominant allele A and B then
because of mutation it will change into recessive a and b. Analytics shows that most of the
genes which are being produce as a result of mutation are mostly heterogeneous and
recessive.
3. There are various kinds of mutations like point mutation in which targets only one
nucleotide like only one base pair is substituted in it with another base pair.
The mutations that are deleterious rarely occurs in nature. But as they occur
constantly in each generation can result in large number of back mutation which
cause more aggregation of allele in a population. This is known as mutational
pressure.
Selection
Selection cause a change in gene frequency by selecting individulas with greater
adaptability and thus reducing their genetic variability.
It work in such a way that desired individuals are slelected thus their allelic frequency within
a population increses and reducing the frequency of other allels which are not desirable.
Environmental factors plays a major role in perfofrming selection on phenotypic basis and
varaition in environnment causes a change in the phenotype of plant speies thus make it
suitable for selection as survival of the fittest is preferrable through natural selection. In this
way frequency of desired alleles increase within a population and undesirale alleles will
decrese . After some generations ,the new allele becomes a part of that generation which then
constitue a new genotype and phenotype ,which reuslts in the formation of new species.
Natural selection
Artificial selection
Non random mating :
Most of the times individuals reproduce sexually by random
mating.Like an individual mate with other individual based on its
phentoypic characteristics like height , colour,etc to but in some
casses individual undergo inbreeding and outbreeding.Which
results in not maintaing the balance and thus causes a change in
gene frequency. These both results in evolutionary changes .Like in
outbreeding different alleles from different individuals combines
together which result in the production of offspring which is
different from parental generation.However inbreeidng is as a reuslt
of self pollination results in the maintainance of uniformity among
individual and thu prevents changes in gene frequency.
