[Music] we'll continue this chapter of reproduction and development by visiting a farm in space but instead of growing potatoes like in that movie about martians with Matt Damon we'll see how eggs are made in real time so let's get cracking and talk about oogenesis oogenesis is the process where mature female gtes or OVA are made from germ cells oogenesis occurs in the outermost lay of the ovaries and unlike spermatogenesis begins before birth to show that we'll draw this pregnant cow in the developing fetus primordial germ cells originate from the Primitive streak and migrate through the hind gut before reaching the gonadal rid which becomes the gonads in the absence of a y chromosome the gonads become fetal ovaries and the primordial germ cells undergo mitosis producing immature diploid cells called oogonia oogonia then multiply via mitosis between weeks 9 to 22 of gestation by week 24 the female ovaries will have up to 7 million oogonia unfortunately most of these oogonia will um die and the rest turn into primary oyes by the time of birth there'll be about 2 million primary oyes depicted by these golden eggs dang I wish I had 2 million golden eggs I'd be ecstatic anyways the primary oit then enter meiosis but get arrested during prophase 1 and so they'll remain arrested throughout childhood let these golden eggs locked inside a cage behind the cute cuddly calf serve as a visual reminder all right so now we've reached that long behold awkward period in life adolescence after commencement of ovulation the primary oite completes meiosis 1 producing a haid secondary oosy and our first polar body this silver egg represents the secondary oite and the shriveled egg nearby well that's our first polar body but I sometimes switch out polar with dead because that's where this one ends up rest in peace my friend you live to polarizing life oh okay not really so these cells have just one set of chromosomes after completing one round of cell division to put in another way they're haid hence the single horizontal stripes the secondary oite then enters meiosis 2 but gets arrested in metaphase 2 again this is depicted by the silver eggs locked inside a metal cage metal for metaphase 2 they're prone to trouble I know but hear me out because the last step is a favorite of mine fertilization I don't know about you but fertilization that is a beautiful thing man it's where it all comes together fertilization allows the secondary oosy to finally complete meiosis 2 producing a mature ovom and our second polar body during fertilization the haid sperm pronucleus fuses with the haid female pronucleus forming a diploid zygote with two full sets of chromosomes and that's my cue to exit okay okay no more yolks instead check out this Speedy summary oogenesis is the process where mature female gtes or OVA are made from germ cells oogenesis starts before birth first primordial germ cells differentiate into oogonia which proliferate via mitosis producing more oogonia next oogonia become primary oyes they enter meiosis but get arrested during profase 1 they'll remain this way throughout childhood then from puberty to menopause the primary oyes complete meiosis 1 producing a haid secondary oosy and our first polar body the secondary oite gets arrested in metaphase 2 until fertilization which allows the secondary oosy to complete meiosis producing a mature ovam in second polar body the haid ovam then fuses with the haid sperm creating a diploid zygote