February 21, 2019 Thursday
Bedtime Story
Homologous Recombination and Meiosis
DNA breaks that involve rupture of both the
strands simultaneously are known as (quite unimaginatively) double-strand
breaks.
Although homologous recombination is a
cellular method to solve the problem of double-stand breaks we are more
concerned with the effect that it has on the production of sperms or eggs that
are together known as gametes.
It is possible, though not certain, that
during the course of evolution chromosomal crossover was primarily a DNA repair
mechanism that accidentally got incorporated in the pachytene phase of prophase
I of meiosis.
The entire process of meiosis (which is a
Greek word for lessening and therefore very apt as you see shortly), involves
production of four haploid cells from one diploid parent cell each of whom are
genetically distinct and unique from the parent cell that gave rise to them and
eventually form the gametes for the organism.
In human male apes this single cycle of
meiosis or sperm formation in the testes takes around 74 hours (in females
meiosis and thereby egg formation is far more complex as everything is in their
case and this has not been said in any deprecatory sense or intent).
As an aside it may surprise some of you
that human apes may be the only species on this planet whose fairer counterpart
consider it normal to live decades after menopause (and if desirous of it to
enjoy hassle-free sex too).
This has allowed grandmothers to rear the
children of their children thereby increasing their survival rate manifold and
giving our species a tremendous advantage over other species.
It might come equally as a revelation to
some of you to know (against all the prevailing notions about glorious past)
that during the time of traditional medicines such as ayurveda, naturopathy and
Hippocratic humorism members of our species rarely survived beyond menopause
and middle age succumbing beforehand to disease, microbial pathogens, accidents
and predators.
A simple rabid dog bite would be fatal
those days (the killer being RNA Lyssavirus in this case which is both neuroinvasive
and neurovirulent).
For the sake of better understanding
therefore meiosis has been classified into stages which we need not go into
since it is available at the tip of your fingers quite literally.
Minute details of this fundamental
biological mechanism are also invariably tested in all the competitive exams
that serve as an entrance portal to any profession remotely connected with
biology.
The crossing-over was first discovered by a
Belgian priest and cytologist by the name of Frans A. Janssens who published
his finding in a paper in the year of 1909 in the first journal of cytology
called La Cellule.
(You would recall that it was yet another
Belgian priest by the name of Georges Lemaître who had first proposed on
theoretical grounds that our universe must be expanding).
He called crossing-over “chiasmatypie” and
his 1909 paper was titled “The theory of the Chiasmatypie”.
Stay tuned to the voice of an
average story storytelling chimpanzee or login at http://panarrans.blogspot.com
Good night Mon Ami and my fellow cousin ape.
Advertisements
Another great educator and a teacher that I am aware of is
Professor Subhashish Chattopadhyay in Bangalore, India.
While I narrate stories, Professor Subhashish an electronic
engineer and a former professor at BARC, does and teaches real mathematics and
physics.
He started the participation of Indian students at the
International Physics Olympiad.
Do visit him here:
All his books can be downloaded for free through this link:
For edutainment and English education of your children, I
recommend this large collection of Halloween Songs for Kids:
No comments:
Post a Comment