Hardy Weinberg Principle Examples Video Lecture - Biology Class 12 - NEET

hello friends this video on evolution
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calm no more fear from exam so let us
look at the examples so example 1 it
says that with it a population of
butterflies the color brown which is
your own if I capital B is dominant over
the color white which is small D and 40%
of the butterflies are white so that
means it is telling these butterflies
are white and white butterflies will be
denoted by which genotype swampy morning
so homozygous recessive value is being
given to you calculate the following the
percentage of butterflies in the
population that are heterozygous and the
frequency of the homozygous dominant
individual as I have mentioned before if
you know homozygous recessive value you
can calculate both heterozygous as well
as homozygous dominant so we will make
use of it now in this question what is
given the value now what do we know from
Tai Chi Weinberg principle first letter
stands right there
so from hardy-weinberg principle we know
two things so the first thing is that
the Ellie's the frequency of athletes is
going to be constant over generations
that is P plus Q is equal to one that is
one thing we know the other thing which
we know is P Square plus 2pq plus q
square is equal to one here this will
tell you the frequency of heterozygous
and this will tell you the frequency of
homozygous dominant right and this is
going to tell you the frequency or
homozygous recessive so this is all that
we know from hardy-weinberg principle
now in this question forty percent of
the butterflies are white what does that
mean
this means the frequency or the
homozygous recessive is forty percent
that means it actually gave you the
value of this so I asked for the
question
two squared is equal to 40% and what
does 40% it is 0.4 so from this you can
calculate the value of Q which is going
to be square root of 0.4 and that is
equal to zero point six three
approximately right so now you've got
the value of Q now with Q you can find
out the value of P therefore P will be
equal to one minus Q so that is one
minus 0.63 which is going to be zero
point three seven so now you know Q and
you also know P therefore you can
calculate the frequency of homozygous
dominant
now first part asks about the
heterozygous so you have to calculate
the percentage of heterozygous so
heterozygous frequency is given by 2 PQ
so 2 PQ is equal to 2 into P is zero
point three seven and Q is zero point
six three so this is equal to 0.47 so if
you want to write it in terms of
percentage this is what will be equal to
47 percent so this is the percentage of
the population at a heterozygous the
second part of the question asked the
frequency of homozygous dominant
individuals so for homozygous dominant
homozygous dominant we will be given by
T Square and P is zero point three seven
so see your point three seven into zero
point three seven that is equal to 0.14
so this is where to be the frequency of
homozygous dominant individuals right so
this is how we can actually calculate
what would be the percentage of
heterozygous what would be the
percentage of homozygous dominant if we
know the percentage of homozygous
recessive so let us look at another
example there are hundred students in a
class ninety-six did well in the course
whereas for blue it totally and received
a grade of F in the highly unlikely
event that these genes are
genetic rather than environmental if
these traits involve dominant and
recessive and yields and if the four
represent represent the frequency of the
homozygous the recessive condition
please calculate the following so again
the homozygous recessive condition is
being given and almost I guess recessive
is denoted by which value of the
equation of hardy-weinberg principle so
homozygous recessive is given by Q
square so as for the question Q square
is given as 4% which is equal to 0.04
that is Q square so what we need to
calculate in a we have to calculate the
frequency of the recessive and E so
frequency of the recessive allele is
denoted by Q so Q will be equal to under
root of Q square that is under root or
0.04 which is equal to 0.2 so this would
be the frequency of recessive allele
frequency of the dominant allele that is
P so P plus Q is always equal to one so
P will be 1 minus Q that is 1 minus 0.2
which is equal to 0.8 and in the third
part we have to calculate the frequency
of heterozygous individual and that is
given by 2 P 2 so this will be 2 P 2
that is 2 into P is 0.8 into Q is zero
point 2 so this will be equal to 0.32 so
this is how we can calculate the various
frequencies of different alleles so I am
hope that by now you understood the
concept of hardy-weinberg principle let
us look at this example to see how the
frequency of genes can change over a
period of time so we will use the same
example of Beatles for better
understanding so let us suppose in this
locality you have only the red Beatles
so these red Beatles they reproduce
amongst themselves and the population of
red Beatles in
they are due to mutation a single being
bitten and spawned but this green beetle
gives the survival advantage in the way
then it is not being caught by the
Predators and as a result what happens
the green beetles are always saved from
the Predators but the Predators keep on
eating the red beetles as a result the
population of the red beetles keep on
decreasing and at the same time not due
to natural selection
due to the survival advantage of the
green beetles the population of green
beetles keep increasing now over a
period of time it is seen that the red
beetles are completely gone and they are
all replaced by the green beetles so
from this we see that the green beetles
evolved from the red beetle so the
frequency of any is changed
so then if the red beetles was denoted
by some le for example same a so that a
has reduced so the frequency of a has
reduced but at the same time the
frequency of B has increased that is the
allele which represents the green beetle
so that has increased so the total of
the some of the area is this total
frequency of the alleles will remain
constant now let us suppose over a
period of time
suddenly a blue beetle has appeared and
this blue beetles form as a result of
variation which is again due to mutation
so let us suppose this blue pickle is
like something which doesn't which is
very rare and suddenly it has come up
due to some mutation now in this case
the blue color doesn't have any survival
advantage as such but since this blue
beetle exists there so what do u beetles
have formed as a result of
reproduction because sometimes there are
chances that if this beetle is blue
maybe when this undergoes reproduction
with some other because there are
chances that a blue because might
perform so even though their population
did not increase much but you have some
two three blue beetles were there now it
is suppose due to some accident for
example a huge animal like elephant or
lion or something like that
suddenly steps in on this portion of the
area now when they step in what happens
all the green beetles get killed so this
is just this happens just by chance so
it is not that the elephant
intentionally killed all the green
beetles it just stepped in somewhere and
just in that area all the green beetles
were there so what happened all the
green beetles are killed at once so
their population drastically reduced now
what are we left with we are just left
with a few blue beetles but over a
period of time these blue beetles will
then undergo reproduction amongst dead
cells and the population of Blue Beetle
will increase so what happened here this
accidental survival of the blue ones was
an example of genetic drift and the
survival of the green ones well it's an
example of natural selection now but if
you look from the beginning till the end
what happened what happened was that
initially the frequency of the red
beetle was wood then the frequency of
the green beetle was Road and then again
a time came when the frequency of the
Blue Beetle was more so we can say that
the frequency of an inherited trait or
the frequency of a certain gene can
change over generation but the total
frequencies of the alleles will always
remain constant so even though the red
eatle is being replaced by the green
beetle that is fine but in each
generation the total frequencies that is
the sum of the frequencies of all the
enols
will always be equal to one so this was
what was told by the hardy-weinberg
principle and whenever you see that The
Hiding Weinberg principle is being
deviated it is not being followed
that means evolution is taking place so
in this case if you see when you try to
compare these generations together for
example if you just consider the
generation red bear only red beetles
were there so in that case your
hardy-weinberg equilibrium I told true
but when the Reds are being replaced by
the green ones your hand Weinberg
principle equilibrium will not hold true
because now you actually have some green
beetles and some red beetles and your
equilibrium is spoiled so that means
evolution is taking place so whenever
there is a deviation from hardy-weinberg
principle wherever you see that P Square
plus 2pq plus q square is equal to 1 is
not being satisfied that means evolution
is taking place now some of the factors
which affect hardy-weinberg principle
are going to be almost the same factors
which cause evolution so the disturbance
and Hardy Weinberg equilibrium indicates
evolutionary change gene migration so
organisms moving in bunch from one place
to another that causes a change in the
equilibrium both at the place from where
they are moving and also at the place
where they are getting into genetic
drift as we saw in the previous example
that when genetic drift is there the
green beetle what will be placed with
blue beetles so now when this happens
what happens that entire equilibrium is
spoiled because the genes which were
responsible for the green color they
drastically decrease mutations so
because wherever mutations are
tens of change happens and therefore
evolution happens genetic recombination
so all these factors are basically the
factors which cause evolution and these
are the factors which disturb the ID
mindful equilibrium as well so I hope
now you've got to understand why we
dispersed about Heidi Weinberg
equilibrium here last but not the least
natural selection again because natural
selection is one of the primary factors
which cause equally which cause
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