Questions 1 - Principles of Inheritance and Evolution Video Lecture - NEET

hello friends this video on principles
of inheritance part 44 is brought to you
by exam table no more fear from exam so
this was all about with chromosomal
disorders and with this we end our
discussion on the genetic disorders so I
think we have reached towards the end of
this lesson and now it is time for
questions so let us look at some of the
question to see if you have actually
understood the lesson well or not so let
us look at the first question it says
and diploid organism is heterozygous for
food looks like how many times of
gavin's can be produced so now when you
see a diploid organism so what do you
infer out of it
so let us try to understand it word by
word so I say deploy that means it has
got two sets of chromosomes right so
they have two sets of chromosomes so
that is what we mean like deployed then
it says it is heterozygous that means
the two alleles are going to be
different so when I say heterozygous on
a particular gene the allelic parents
are going to be different so here we can
say different
ellee's for a gene then say for for
locals so ours is locust locust is
nothing but the position on the
chromosome so let me suppose this is the
chromosome so here it is trying to say
that it has four different genes on four
different locations on the same
chromosome for four traits or four four
genes and they are all heterozygous that
means the corresponding and heels or the
other gene I am going to be different so
if here it is let us say p q r s f PQRS
are the genes which are located on the
four locus of the chromosome then they
are corresponding genes on the whole of
the score
going to this one piece or use one eye
and someone s because this is a gross I
guess and why do we have to to care
because of this diploid so it is going
to have new set of chromosomes since it
is deployed so we have two sets of
chromosomes
since it is heterozygous so they are
different capital T small a capital to
small Q since it has all look closer
locus that is why it has four genes 1.4
locations on the same chromosome that is
for contrasting characters or poor genes
whatever you want right so now we have
to find out how many types of gametes
can be produced out of it so basically
what we have we have an organism or we
have an organism with four contrasting
traits like this correct okay so now
what does the various formulations
possible now you remember when I used to
talk about a dihybrid cross a quick
recap so when I used to talk about a
dihybrid cross what I used to say in
dihybrid cross we consider two
contrasting drinks okay so when we
consider two contrasting tree each
gamete every gamete should have one
letter represent in each tree for
example if we are talking about the
speed and we are considering nutrients
that is the shape of the seal and the
color of the seed in each damage you
have one letter representing the shape
of the stick and one letter representing
the color opposite so if I say ry that
means it is around to see which is
yellow being valid if I say I happen to
mine I mean it is a wrinkled seat which
is the other way but if I say are my I
mean it is a little too green better so
basically the number of trades which you
are considering for each trait you
should have one representative in a
gamete so in this case your gamete will
have how many letters because then you
have four traits right you actually
bring more contrasting traits so each
gamete should have four legged each
letter will present in each trait right
so how many such
for metals can you create out of this
for example this is one possibility
similarly this this can be one
possibility so these are the two extreme
possibilities there are many
possibilities where P is that will
choose fall I will small Nexus 4 so that
means you can actually find out many
combinations now how do you know that
how many populations and in find out
because if you actually start finding
out all the cup population manually it
is going to take a lot and so how do you
go how many combinations will be
possible now it is very simple we use
the simple combination technique so we
know that it will be up for each gamete
will be a four letter word right now
this first position have been taken up
by how many times scored being capital P
so two possible values the second
position Q can be taken up by how many
values two possible values third
position I can be taken up by how many
values two possible and it is nes can't
be making abutting possible values now
you might think like all of them how
much you get to it that is 16 so this 16
is the total number of possible
combinations that means total you can
add 16 such combinations out of this
that means 16 granules are possible out
of this diploid organism which is
heterozygous for four contrasting traits
now if you want to verify this just try
it out for an organism with two
contrasting traits so something like
this so if you consider an organism into
podcasting race let us suppose we
consider this one the dihybrid cross
scenario right so in this case each
gamete will should have two letters like
this so this R can take how many values
depending to and scapular and smaller y
and z common values two values swap I
capitalized you multiply them so how we
do how much you get four so four gallons
are possible in this scenario now these
16 gamuts on these four
possible only if they follow the
principle of independent assortment so
only that is this will be true so many
people often find it out with the
formula so if you actually see this
formula is melting point two to the
power n where n is the number of
contrasting traits so you can use that
formula has been but this will apply
only means of independent assortment
increase there is linkage linkage comes
into picture in the number of gametes
will reduce because whenever there's
linkage there the two genes will become
linked and they will always be inherited
together so you are not for the
combinations will reduce and therefore
the number of gametes will reduce so
this 16 Gammons are going to be possible
only in case of independent assortment
okay so I hope this concept is clear so
please do not memorize the formula P to
the power n just for the heck of it try
to understand how this is happening and
this is the actual logic then how you
get to know that how many rabbits will
be produced let us look at question
number two let us look at question
number two it says define and design a
test cross so how do we define a test
cross first of all now I have mentioned
this before also the test crosses are
linked but cross between an individual
with an unknown genotype with a
homozygous recessive parent know what
happens now when you get the output of
this cross that can tell you whether the
underlying was heterozygous or this was
almost I go so how do you know that if
the protein is 50% dominant and 50%
recessive that means the genotype under
genotype is heterozygous that's because
the heterozygous will have both the
trades one will be dominant one will be
recessive so one trait will remain
hidden right which get expressed in the
next generation the test cross it gets
expressed in the ratio of complicity but
if the progeny is all hundred percent
dominant that means the unknown genotype
is homozygous so let us try to perform
fetch cross and see if it turns out
to entry selective suppose in the first
case we assume that the this is the
unknown genotype which we now know is a
heterozygous so we are just trying to
see if we get a 50/50 a dominant
recessive output so this will be crossed
with the homozygous recessive so what
are the gametes that will be formed from
here capital T spawn T and here you will
get only squaddies so these are the
various possible combinations in this
case okay so what will be the possible
offsprings are possible outcomes of this
cross so this is not possible
output so in this case this thing's
going to be dominant right these are
going to be gone so let us suppose we
have taken tall and dark as the change
and this is going to be you are right
so if you see out in the output 50% of
them are tall and 50% of them are dot so
50% dominant and 50% recessive so this
shows that the unknown genotype is head
of all science
now let us loop perform the second
scenario when we take the unknown
genotype as homozygous so if don
genotype is homozygous it can produce
capital t gamuts and this will produce
quality so in that is the possible
outcomes out of these combinations could
be all heterozygous but at the same time
all of them are heterozygous but all of
these are tall so you actually get the
output as hundred percent dominant so we
know that the unknown genotype is
homozygous so this is how H cross is
designed and this is a test cross this
is what we infer for a test run that is
why the name is test cross because it is
used test if the unknown zero type is
homozygous or heterozygous thank you
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