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In 1943, T.M. Sonneborn, for the first
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time, reported a new mechanism of
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In his words, "The present paper reports
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a previously unknown system of relations
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between a gene and a cytoplasmic
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substance, both of which are required
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for the development of an hereditary
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The mechanism was called the cytoplasmic
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inheritance, the inheritance of kappa
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particles in Paramecium aurelia.
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In this video, we'll be discussing
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the cytoplasmic inheritance of kappa
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particle. What are kappa particles and
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why is it called as cytoplasmic
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inheritance within 5 to 10 minutes?
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consider subscribing to this channel.
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Let's move into the detail of this
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Point number one, there are two
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Paramecium strains. The first one is
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called the killer Paramecium, and the
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second one is called the sensitive
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To become a killer, the Paramecium
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should have two prerequisites. First
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one, a nuclear gene, which is called as
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capital K gene, either in homozygous,
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that is capital K capital K, or
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heterozygous condition, capital K small
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Along with that, there should be a
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cytoplasmic particle,
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which is called as kappa particle. These
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two things are essential for a
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Paramecium to become killer.
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What is actually happening is this kappa
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particle secretes a toxin, which is
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called as paramecin, and this toxin,
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upon ingestion by the sensitive
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Paramecium, this is toxic to the
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sensitive Paramecium, causing its death
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That's why this is called as sensitive
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Paramecium. Whereas, a sensitive
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Paramecium has small k small k, that
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makes it sensitive, no dominant K gene.
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Even this Paramecium has capital K
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capital K or capital K small k,
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homozygous or heterozygous condition,
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Without kappa particle, it remains
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And finally, with kappa particle, if
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this sensitive paramecium has a
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then also it becomes sensitive. In
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short, to become a killer paramecium,
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two things are essential. First, a
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dominant K gene along with kappa
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Both are essential to become a killer
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paramecium. Now, let us see the summary
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of the study carried out by Sonneborn.
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He found out that during a brief
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conjugation between killer paramecium
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and sensitive paramecium,
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killer paramecium capital K capital K,
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whereas sensitive paramecium capital K
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small k, killer has kappa particle also.
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During the conjugation, there is no
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during brief conjugation. This K gene is
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and the small K gene is transferred to
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this killer paramecium. Now, the F1
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exconjugants are the killer paramecium
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becomes capital K small k, that is
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heterozygous condition. The small K gene
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is transferred from the sensitive
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whereas sensitive paramecium becomes
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capital K small k in heterozygous
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condition. This capital K is transferred
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from killer paramecium, but it remains
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sensitive as there is no transfer of
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kappa particles. So, killer remained
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killer as it has dominant K gene along
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with kappa particle, whereas sensitive
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remains sensitive as it has only the
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dominant gene, but no kappa particle.
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So, there is no cytoplasmic exchange,
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only nuclear exchange takes place during
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this brief conjugation.
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Now, let us see the second conjugation.
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In prolonged conjugation, he found out
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this killer paramecium and sensitive
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paramecium, during prolonged
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conjugation, there is both cytoplasmic
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exchange and nuclear exchange. This
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capital K is transferred to the
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and kappa particle is also transferred
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by the formation of a cytoplasmic bridge
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during prolonged conjugation.
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As a result, the F1 exconjugants are the
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small k and capital K, that is
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heterozygous condition. There is a
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dominant K gene along with kappa
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particle. Killer remain killer, whereas
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the sensitive Paramecium is transformed
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into killer Paramecium as it has the
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capital K gene that is transferred by
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the nuclear transfer. And also there is
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cytoplasmic transfer. There is
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cytoplasmic exchange. Therefore, kappa
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particles are also transferred from this
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killer Paramecium to the sensitive
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Paramecium. That's why
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So, the trait is actually transferred
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via cytoplasm. That's why this is called
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as cytoplasmic transfer. Let me
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summarize. During brief conjugation
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between a killer Paramecium and
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sensitive Paramecium,
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both remains the same. The killer
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remains the killer and sensitive remains
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the sensitive as only nuclear exchange
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But during a prolonged conjugation
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between killer Paramecium and sensitive
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there is both nuclear exchange and
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cytoplasmic exchange. So, along with
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transfer of capital K gene,
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kappa particles are also transferred.
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the sensitive is transformed into
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And that happened during the cytoplasmic
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Now, let me make it more clear.
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So, what is cytoplasmic inheritance?
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It's a type of genetic transmission
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where traits are inherited through the
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genes located in the cytoplasm rather
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So, in killer Paramecium, there is
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capital K gene that is residing in the
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nucleus, whereas kappa particles are
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essential. So, kappa particles
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is located in the cytoplasm.
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And this particle, now we know that this
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is actually an endosymbiotic bacteria,
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Caedibacter taeniospiralis, living
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within the cytoplasm of Paramecium.
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So, this bacteria has genes
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that secretes toxin called paramecin
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sensitive Paramecium.
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Then, the host must have nuclear K gene.
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The K gene must be essential for making
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this paramecin killer. Kappa particle
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alone cannot make this paramecin killer.
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As this K gene is essential for the
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multiplication and survival of kappa
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Now, why it is called as cytoplasmic
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The reason is the physical location of
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that determines the killer trait, that
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is inside the cell cytoplasm, not inside
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the nucleus. And it does not follow
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Mendelian laws. So, cytoplasmic transfer
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along with nuclear transfer only
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transforms a sensitive Paramecium to a
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killer Paramecium. That means the
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physical location of the genetic factor
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that determines the killer trait is in
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the cell cytoplasm, that is a kappa
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particle. Now, we know that these are
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genes inside this endosymbiotic bacteria
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that is located in the cytoplasm.
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So, hope you are clear with the
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cytoplasmic inheritance of inheritance
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of kappa particles in Paramecium
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Hope you are benefited from this video.
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Take care. Stay blessed. Thanks for
