Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

CONJUGATION IN PARAMECIUM
Conjugation (sexual reproduction)


Frequently referred to as sexual reproduction
...




It is a unique process in which 2 individuals separates soon after the exchange of their
nuclear materials
...


Figure: Steps of paramecium’s conjugation
...
The following is related
to P
...




In conjugation (sexual reproduction) the two paramaecia or preconjugates from 2 different
mating types of the same variety come in contact ventrally and unite through the edges of
their oral groove
...




They then stop feeding and their buccal structure disappears
...




Now, at this stage, they are called gametocytes or conjugant
...




The macronucleus simply breaks up into fragments, which are later absorbed by the
cytoplasm
...




And forms 4 haploid daughter micronuclei
...




Of these, the smaller one is the active male migratory pro-nucleus, whereas the larger one
is the stationary female pro-nucleus
...




The nucleus of the zygote is diploid and is called amphinucleus and this type of mixing of
two nuclei from different individuals is called amphimixis
...
separate and now called exconjugants
...




while remaining micronucleus divides with binary fission of exconjugants
...




The micronucleus again divides with the division of each daughter paramecium, forming 2
individuals each containing one macronucleus and one micronucleus
...


Factor and condition of conjugation
Conjugation is very complex physiologically
...
some of them are:


Occurs under an unfavorable condition like starvation or shortage of food and particular
bacterial diet or certain chemicals
...




Occurs when there is a change in the physiological condition of paramecia, it occurs between
such individuals which are smaller in size (210 µm long) than the normal individuals (300350 µm long)
...




Conjugation usually starts early morning and continued till afternoon
...




The pairing conjugants are isogamous and there is no morphological sexual dimorphism into
male and female conjugants
...
It never
takes place among the members of a ‘pure line’, that is among the descendants of a single
individual
...


Significance of conjugation
A clone will die out if nuclear reorganization does not occur, but the clone can be rejuvenated to
regain its former vigor by nuclear arrangement, this is brought about by conjugation
...
The significance of conjugation is described
below:


If binary fission continues repeatedly for a longer period of time, Paramecium loses its vigor
and physiologically depressed, reduces in size, ceases to multiply, degenerates in the
organization, and eventually die
...

However, Woodruff and Jennings do not support the view that conjugation helps in
rejuvenescence
...




There is no distinction of sex in conjugation though only paramecia of different mating types
of the same variety will conjugate
...




Conjugation ensures the inherited variation
...
So, all paramecium has the same
inheritance
...




Conjugation brings about the formation of the correct number of chromosome in the
macronucleus, so the race is renewed in vigor and vitality to accelerate the metabolic
activities but in binary fission chromosome of the macronucleus were distributed at random
to the daughter cell, continued binary fission had made the clone weak with some structural
abnormalities

---