Today I thought that often when I write I talk about life. But of how this originates, in organisms with sexual reproduction, I never talked about it. Speaking of the microscopic aspect, and therefore the cellular one, we can refer to the meiotic process. Meiosis is called sexual reproduction. The particular thing about this type of reproduction (independently gametic, zygotic or intermediate) is the gene mixing that takes place in it. In the scientific world we talk about Crossing-over. This is a phenomenon that occurs in one of the phases of meiosis, specifically during the pachitene of prophase 1.

So why are we all different? Why two individuals can generate different organisms (in genetic and phenotipic terms)? The answer is in this process, that allows the genetic exchange between chromosomes. Or rather, the exchange between non-sibling chromatids but belonging to homologous chromosomes (ie morphologically identical chromosomes, one from the mother and the other from the father) takes place. Why evolution has generated this type of reproduction is not so obvious. The advantages of sex are many:

• Environmental adaptation: the presence of multiple genomes allows the survival of some in adverse environmental conditions;
• Resistance to pathogens: with a more diversified genes, one of the various allelic combinations will surely be able to respond to the attack of pathogens;
• Red queen hypothesis: “sex is necessary to stay in competition against one’s parasites”

Of course, sex also has its disadvantages, such as the high energy expenditure and the birth of the concept of death. Why the latter? Because, in fact, the organisms that have asexual reproduction generate clones that make parents essentially immortal. With sex instead, new individuals are always generated and the parents who die, really die!!!

This is only a small step towards the discovery of sex, the rest is yours. Do not be adverse, it is interesting to understand how our permanence on earth is still possible. Go back to when you were 2 small cells that joined together and make this journey into the world of meiosis.

P.S.: When I talk about sex I intend to discover the meiotic process. Indeed it may seem ambiguous.

Maria Bruno