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Hi friends, in this video we have an
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interesting topic that is sex
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determination in plants. Do plants have
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sex determination as in humans, the XY
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mechanism or some other mechanisms?
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So, this is a classical study that was
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conducted during the '50s
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considered as a crucial milestone in the
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study of plant genetics. And we'll be
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discussing this within 5 to 10 minutes.
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The study was conducted by team of
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under the leadership of Warmke and
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Westergaard in the 1950s. The plant was
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Melandrium album. First, let us
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summarize their findings before moving
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Plant is dioecious. That means there is
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a male plant and a female plant.
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They found out that in this plant there
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is an active Y chromosome just as in
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The diploid number of plant is 24.
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The other synonym of this plant is
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Silene latifolia. At that time it was
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called Melandrium album.
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So, this is the female plant just like
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humans, it is XX whereas male plant is
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XY. Female plant is homogametic. It
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produces one type of gamete, that is X
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gamete. Whereas male plant is
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heterogametic, produces X and Y sperms.
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And the offsprings are produced in equal
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number, that is 50% will be female and
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Now, let us see how this works. And they
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found out that the Y chromosome
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in Melandrium is significantly larger
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compared to the X chromosome.
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And they identified specific regions on
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Y chromosome and X chromosomes that
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actually determines the sex of the
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plant. The chromosome is submetacentric.
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A short P arm and a long Q arm. The
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first region or first segment contains
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that suppresses female development
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or inhibits female organ development.
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The second region on the Y chromosome
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is a male initiating region
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or that initiates male reproductive
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organ development. And the third region
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in the Q arm is the male maturing
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region. It controls anther maturation
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And the fourth region is a segment four,
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which is a homologous region that pairs
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during meiosis with the X chromosome.
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So, these are the four regions they
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identified on the Y chromosome of
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Whereas in X chromosome, there is an
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homologous region, a pseudoautosomal
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region that pairs with Y chromosome
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Then, there is an X specific region,
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that is a female promoting region that
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contains genes that promotes the
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development of gynoecium.
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So, these are the regions on X
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chromosome. As we mentioned, X
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chromosome is smaller compared to Y
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Now, let us see how these regions
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affects the development or determines
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the sex of the plant. First case, as you
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see, this is Y chromosome which is
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intact and X chromosome.
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So, Y chromosome, the segment one will
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the production of female reproductive
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structure. So, this is a normal male
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The stamens develop and mature as all
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four segments in the Y chromosome is
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And this is a normal female. There is no
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Y chromosome. There is only X chromosome
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or XX. So, the segment in the X specific
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genes promote the gynoecium development
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or carpel development. And this is the
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And they did certain mutations to find
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out the functions of each regions. And
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in the third case they mutated the first
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segment. As we know, this first segment
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in suppressing female reproductive
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The genes in the first segment is
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involved in suppressing
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the formation of female reproductive
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system. So, this is deleted so that
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there won't be any suppression.
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Gynoecium or carpel grows along with
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stamens. Therefore, the plant will be
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bisexual or hermaphrodite.
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This is how they identified that the
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first segment or genes in the first
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segment is actually inhibiting the
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growth of the female reproductive
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structure or gynoecium.
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And the final case is the second region.
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They mutated the second region. As we
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know, the second region is involved
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in the formation of male reproductive
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structure or male initiating region. So,
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second region is mutated. First region
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is active, that will suppress the
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formation of carpel. Second region is
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suppressed or mutated, that will inhibit
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the formation of male reproductive
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structure or anthers. Then the flower
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will be asexual without anthers or
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That lead to asexual flowers.
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And they found out that this Y
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chromosome is actually determining the
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sex of the plant in Melandrium.
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Further, they found out that there is a
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dominance of Y chromosome even in
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polyploids. And this is a female
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>> autosomes and X chromosomes.
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They showed that Y chromosome is so
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dominant that even in polyploids, as you
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see, the presence of a single Y
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chromosome will make it
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male even in triploid condition
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or polyploid condition.
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But later, hermaphrodites in extreme
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cases, if the dosage of four X
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chromosomes presence of four X
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overcomes the single Y chromosome.
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Then the plant become bisexual or
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Hope you are clear. Take care. Stay
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blessed. Thank you so much. You are with
