"Well to make a baby, he fautdéjà a dad and a mom" ... Cettephrase classic is often the first step in a more or less longueexplication that many parents give their child. This assertion is easily verified, and since ancient onpense he must wear an exchange of "fluid" between hommeet woman to give birth to a new individual, and although viergemarie " Holy Mother of God, "complicating the problem, the affairesemble heard. But the relative share of each parent in the "design" of a new individual is to explain ... In today's context Revisionof bioethics legislation, I propose a rereading of modern conceptsovistes. Let's start by seeing what it is.
Oviste cons animalcules.
Although the importance of deuxparents quickly perceived the "theory of fertilization" n'estformalisée in 1900 by German Oskar Hertwig. Meanwhile two camps: the animalcules one hand, who believe that the sperm contains unbeing miniature preformed homunculus or
(see engraving above cons), and they envisage that the egg chamber andspreadsthrough development. Ovists the other hand, who is the ovulequi essential for procreation, semen and plays a role of activator. And in some cases such as parthenogenesis, it is not even necessary! This theory is more relevant today as it also entails the individual existenced'un preformed inside the egg. But see how the prépondérancede the egg in the development proves relevant.
Parthenogenesis and relevance ovism.
Parthenogenesis is the developmentof individual from an unfertilized egg. The first example natural étéobservé by Bonnet in 1745 which won several generations of aphids dufusain by isolating females from birth. The presence of réservesnutritives only the female gamete (Egg) that makes this possible and how dereproduction unthinkable from a sperm (gamètemâle). And yes the eggs are usually the most volumineusesde cell body, you only see the size of the egg yolk to it rendrecompte! If existenaturellement parthenogenesis in certain groups, can also déclencherartificiellement, as is was done in mice in 2004. Following oocyte fusionde two nuclei (one mutated gene), it was the first time obtenirpour 2 mice without a father ...
[ An aphid and its progeny pathénogénétique ]
The unequal participation of chaquegamète.
Ultimately brings lespermatozoïde during fertilization? Well if we look closer, pasgrand anything ... Of course there is the nucleus that contains the genetic, ceques is still not nothing: for every pair of chromosomeshomologues one of them comes from the sperm ;! During parthenogenesis several solutions are made to cemanque address: fusion with another cell, removing a phase divisioncellulaire etc.. The second element is given a centriole: a cylindrical petitestructure necessary for the proper arrangement of the components cellulelors division. In the end no other element does not fit into the oocyte, and 100% of the mitochondria of our cells are of maternal origin! So a cytoplasmic view at least, the large egg sembleeffectivement role, what about a genetic point of view?
[ The "yellow" from the ostrich egg is the largest one known animal cell .]
gynogenesis, androgenesis and gender war ...
It has been said already apporte50% male chromosomes but some findings suggest that genetic cetapport is not functionally equivalent to that of lafemelle. Indeed in some groups of oocytes fertilized by unspermatozoïde can develop without the male genome does participe.Celui it does not fit the maternal genome and is removed: it lagynogenèse. The equivalent with a male genome is androgenesis, it seproduit than in mammals where sperm nucleus fuses with a ovulesans. In this case analogous to the placenta tissue are formed but never a real Nedon embryo. Thus in many cases the génomefemelle alone is sufficient to produce an embryo, while the male genome estinsuffisant! The contribution does not seem equivalent. In fact 200gènes 100 to speak or not according to their parental origin: it lephénomène footprint Genomics.
[ total hydatidiform mole: this cyst from abnormal proliferation of trophoblast is formed by development of a fertilized egg but does not contain a nucleus initially. So there is no embryo. This anomaly relates 0.1 to 0.5% of pregnancies. We're talking large molar ]
An experiment in lasouris tells us a bit more: it is to form a embryongynogénétique (genome female only) and androgenetic embryos (Genome mâleuniquement). It is found that the gynogenesis provides an embryo but not lesstructures extraembryonic for its nutrition. In contrast as mentioned above ona androgenesis gives mainly extraembryonic tissues detype placenta for nutrition of the embryo.
This suggests that genes paternelsfavoriseraient greater resource in utero, while the maternal genes tend to limit cetteexploitation to preserve the body for future reproductions. C'estexemple of sexual conflict where the interests of males and females sontdivergents due to a different investment of resources in lareproduction. There you can imagine, so much more to say about cesujet ... But for our topic of the day the obvious conclusion is that each parent lacontribution fundamentally unequal in lafécondation from there to restore ovism there is only one step and as habitudeje not willing to budge ...
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