Homologous, Heterologous - Heredity & Evolution, CBSE Class 10 Biology Video Lecture

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let us now see what are homologous and
hetero loggers chromosomes so this is
again something new I mean when we are
talking about chromosomes it is
important to know about homologous and
heterologous chromosomes now homologous
chromosomes let us discuss first a set
of one maternal chromosome and one
paternal chromosome that pair up with
each other inside a cell so what are
these homologous chromosomes are Homo
the word homo itself means something
which is similar so a set of one
maternal chromosome that means the
chromosome from mother and one paternal
chromosome that is the chromosome from
father that pair up each other inside a
cell so as I said inside a cell the
chromosomes and right now I am talking
about diploid cells because the only the
diploid cells will have two sets of
chromosomes right so inside the diploid
cell chromosomes will always exist in
pairs
so the pair of chromosomes were one set
is from the mad father the other set is
from the mother and they are similar to
each other they are known as homologous
chromosomes so they are of same size and
shape let us say their form will remain
the same
so such chromosomes are called
homologous chromosomes they be are
corresponding genes governing the same
traits now we know that when you look at
the structure of a chromosome so on the
chromosomes you have genes right and
these genes actually control the
different characters in our body so when
I talk about homologous chromosomes they
are somewhat like this let us suppose
this is one chromosome this is another
chromosome right and here you have the
genes located so such regions so this
region or
the two chromosomes are known as
homologous regions which code for the
same gene that means they both hold for
them same gene now you might ask that
the same gene is present here also but
what are these - these are the sister
chromatids we I have already explained
you right these are known as chrome
athletes this center part which joins
the two chromatids is known as
centromere so the homo Novis of
chromosomes are two different
chromosomes where same genes are present
in the homologous region right so they
have these homologous region basically
consists of different version of the
same gene different version of same gene
right so for let me take an example let
us suppose if I talk about the eye color
right so this is the pattern on
chromosome let us suppose this is the
paternal chromosome and this is the
maternal chromosome see if I am talking
about eye color let us suppose that the
father's eye color is blue and the
mother's eye color is black so in this
case if this gene correspond to the
trade of eye color right so for eye
color both of them will represent brown
both of these so that means the sister
chromatids are exact replicas of each
other but these maternal chromosomes
they will represent blue so these two
will again be representing blue but if
you compare this and this this is also
representing eye color this is also
representing eye color that means both
are representing same gene but different
versions this is representing black
color this is representing blue color so
they are representing different versions
of the same gene so now you understand
what are homologous chromosomes there
are two sets of chromosomes which exist
in pair one contributed by father one
control
my mother and they both are obscene say
same shape and size and they beer jeans
chorus combining the same traits in the
corresponding region that means the gene
governing eye color I present in the
same region similarly let us suppose the
gene governing the skin palate is
present in the same region
similarly the gene governing the earlobe
shape that is also present along the
same region so these are known as
homologous chromosomes so now here in
this picture also you can see the
homologous chromosomes so here the blue
these blue coloured here you can see
this represents the I colored this blue
color represents the father's eye color
this black color represents the mother
eye color so they are known as
homologous chromosomes similarly if I
talk about hetero locus chromosomes that
means different so these are they differ
in shape size and function like in case
of cremona homologous chromosome they
were of same shape and size but here
they have different shapes different
sizes and different functions as well
because here the function was also
similar everything was corresponding to
I'll color but here that is not the case
so they do not belong to the same pairs
so that means if we take one tear of
this chromosome and another pair of some
other chromosome maybe one part is
corresponding to eye color and the other
part is corresponding to skin color so
those kind of chromosomes are known as
hetero logos chromosomes right so the
why I am explaining this is because
these terms homologous and heterologous
will come as we go ahead and discuss
about Mendel's experiments so now we
will know about a new concept called
allele so what are any so now I already
told you the experiment which Mendel had
performed now how do we denote the
traits of different organisms like as I
said there is one tall plant there is
one short plant so how do we denote the
characteristics now the trades are
basically denoted with the help of
letters for example in order to
scribe at all plant maybe I can denote
it by a capital T in order to draw it a
trait that is a dwarf plant so maybe I
can denote it by a small T so that is
how we denote things right so now le is
one member of a pair of gene that occupy
a given position on a homologous
chromosome because we saw that when you
take the example of the homologous
chromosome so what do we see here
so in this envelope is chromosome this
blue color and this dark blue color they
all represent the same gene right so but
they are present in pairs this is one
pair this is one member of the pair this
is another member of the pair so le is
one member of a pair of gene that occupy
a given position on a homologous
chromosome so let us suppose if I denote
let me take an example this way later
suppose if this denotes the blue eye
color which is denoted by a small B let
us suppose if this denotes the black eye
color which is denoted by a capital B so
when you combine together these two
chromosomes because they are existing in
pairs so what do you get small B capital
B so what would be the eye color when
taken together it will be black because
black is the dominant trait right now
each of these pair that means the small
B and this capital B they are separately
known as and any so as here is one
member of a pair of gene that occupy a
given position on a homologous
chromosome via the occupy a given
position because they are going to
correspond to the same trait right
because in homologous chromosome if they
occupy the corresponding positions that
itself means that they are going to
correspond to the same trait now let us
look at some examples let us suppose if
we take this example of the dwarf plant
so how do we denote its allele
now this dwarf plant the plan
in Newton's expand insert in Mendel's
experiment we saw that dwarf was the
recessive trait like it was not
expressed in f1 generation now we have
also studied that when a recessive trait
gets expressed when it inherits the
trade from both of its parents so that
means this plant is dwarf because it has
got a dwarf trait from its both the
parents right so how do we denote this
we do note it has small T small T that
means we are talking about a perfectly
dwarf plant it has received a small T
from one parent and a small T from the
other parent as well so each T is known
as an AV similarly if we are talking
about a tall plant so this tall plant
but for a plant to be tall there are
many possibilities maybe it has got the
toil crate from both the parents maybe
it has got to all trade from one of the
parents so we can represent it as
capital T capital T which shows that it
has received a tall treat from the
father as well as a tall trait from the
mother similarly we can also represent
it as capital T small T that means it
has received a tall trait from one
parent whereas a dwarf trait from
another parent but since storied was
dominant so the plant is thought
similarly we can also represent it as
small T capital T that is it has
received a dwarf trait from the first
parent and a tall trade from the second
parent okay and each of these members I
mean this so we express the
characteristic of any organism in terms
of with the help of letters right now
each of this each member of this pair is
known as an Eddie right so le is a term
which is new to you and this is the
significance of array so let us look at
these examples so these are the examples
of Aziz let us now talk about homozygous
and heterozygous organisms now that we
have spoken about a Leafs we also saw
that there are
ways by which we can express the aliens
or the traits of organisms so based on
what type of alleles are present in an
organism they can be classified into two
types homozygous and heterozygous
homozygous organisms the word homo
always means something related to
similar so these organisms will have
identical alleles that is similar
aerials on homologous chromosomes for
example capital T capital T small T
small T so that means if we talk about a
dwarf plant as I mentioned in the
previous slide also we write it as T T
since it has received the same traits
from both the parents that is why it is
known as a homozygous dwarf plant
certainly if we talk about a tall plant
which has received tall trade from both
the parents we write it as capital T
capital T so both the alleles are
identical so the that is known as a
homozygous tall plant now if self bred
gives rise to offsprings with same
traits that means we all know what is
self breathing self breeding is nothing
but self pollination so self pollination
means if the pollination happens in the
sea in the flower of the same plant so
let us see exactly what happens on sense
breeding now let us suppose that if we
sell pollinate the homozygous tall plant
let install client with another tall
plant so now this tall plant has two
arrays T and T similarly these tall
plant also has two areas now what are
the possibilities which are possible
this T can combine with this this can
also combine with this this can combine
with this or this can combine with this
so what do we see in all the cases we
get homozygous tall plants right so all
tall homozygous so if it is self bred it
gives rise to offsprings with the same
traits that
this is also homozygous tall so they are
also homozygous tall similarly if we
self brain the dwarf plants in that case
also what are the possibilities this
will give out its alleles and these
alleles can combine with in any of these
fashion so in all the cases we get
homozygous Dorf Glantz right so this is
all about and homozygous organism let us
now look at heterozygous organism now I
am sure you know by now what is
heterozygous it is organism with
different alleles for a character on
homologous chromosomes because both are
true for homologous chromosomes because
if only for homologous chromosomes both
the chromosomes will correspond to the
same character right so here what is
that character which we are talking
about in case of these plants we are
talking about the height so whether it
is tall or dwarf it is talking about the
height of the plant so examples of
heterozygous organisms would be small T
capital T or capital T small T so here
we have two different Ally's but since
the tall is a dominant trait so the
plant is tall so if one allele is
dominant the trait will also be dominant
so in case in this case we can say that
these are also known as hybrid
heterozygous is also per hybrid so we
can call these as hybrid tall plants or
heterozygous tall plants right now or if
you're curious to know that what would
happen if we self bred these
heterozygous tall plants so let us try
to see what will happen if we try to
sell bred them let us suppose if capital
T small T is self-pollinated with
capital T small T what will happen it
has these two alleles this has these two
alleles so these are the possibilities
that can occur right so what do we get
in the first option will get capital T
capital T then we will get
capital T small T then we'll get small T
capital T then you'll get small T small
T so in this case if you see the
products are not all identical to the
parent organism right you see that only
two of them are heterozygous so 50% are
heterozygous the remaining two are
homozygous so we can say that the if we
sell bread heterozygous organisms only
50% of them are heterozygous right also
we see that how many of them are tall
and how many of them are short you can
say that this is tall this is also a
tall so this is tall homozygous this is
tall hybrid this is also tall hybrid and
this one is dwarf so what do we see the
result is that reside is three out of
four our toy that means 75% of them at
all one out of four is dwarf that is 25%
of the results are dwarf right okay so
this was all about homozygous and
heterozygous organisms so with this I
think I have covered all the important
basics which was needed to understand
the main des experiments in detail so
let us have a quick review what are the
things that we studied we talked about
what happens during sexual reproduction
how does the chromosome numbers change
we talked about the diploid and haploid
cells we also talked about homologous
hetero locust chromosomes homozygous and
heterozygous organisms and LEDs right so
with this basic knowledge I think we are
good to go
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