eight lecture two it's spermatogenesis spermatogenesis is the process by which we produce haploid sperm cells it starts with this this should say spermatogonia which are the stem cells the first thing that they do is they undergo mitosis and mitosis remember you're going to take a cell that has 23 chromosomes you're going to double the DNA to 48 chromosome 46 chromosomes and then go through the steps of the cell cycle go through the interphase go through mitosis and then you end up dividing the DNA in two and you end up with two identical cells that both have 23 pairs of chromosomes um so the reason they first undergo mitosis is to make sure that they don't run out of stem cells so before it'll go through meiosis each stem cell goes through mitosis to ensure a future reserve of those cells spermatogenesis then its format formation is sperm from the spermatogonium so this is a cross-section of summoned first tubule this will be the lumen in the center into which the sperm when they mature are released and the sperm as they mature are going to move closer to the Lumen you can see that they get smaller and smaller the closer that they get this is another picture the same thing here we have lighted cell and these puzzle piece shaped cells called the sustentacular or sertoli cells and the sperm in various stages of maturation moving into the lumen the diploid primary spermatocytes then undergo meiosis one and they form haploid secondary spermatocytes diploid means that they have 23 pairs of chromosomes haploid means they have 23. remember with the sperm and the Egg the goal is to end up with 23 chromosomes so that when the sperm and egg unite we're back to 23 pairs again one pair from the sperm one of the pair comes from the egg so myos meiosis II produce the haploid um spermatids and the spermatids are going to be connected to one another with cytoplasmic Bridges the final stage is spermatogenesis is spermiogenesis and that's the maturation spermatids into sperm and then the release of sperm from a connection to a sertoli cells called spermiation so spermatogenesis is production of sperm spermiogenesis is the last stage of spermatogenesis where the spermatids mature into sperm and spermiation is the release primary spermatogonia or the stem cells primaries spermatocytes or diploid after meiosis one they're formed into haploids secondary spermatocytes and after meiosis II it's haploid spermatids so here we can see this for matagonium with 46 chromosomes these are diploid they um double the amount of cells of chromosomes that a normal cell does um primary spermatocyte is also diploid then we have the secondary spermatocyte it's haploid the spermatid is haploid and the sperm cell is haploid remember it's matosomatic cells are all the cells in our body except for the sperm and egg and they're all diploid meaning they have 23 pairs of chromosomes one set of the pairs from the mother one set is from the father and we say that each pair is homologous because chromosome one from your dad and chromosome one from your mom are going to have the same linear order of genes they're going to encode for the same things and they'll be on in the same order on that chromosome position one if it's for hair color is going to be the same there's going to be a gene for hair color for both the mother and the father on that chromosome at that position the genes themselves may be different but the position on the chromosome is going to be the same um of those 23 pairs of chromosomes 23 pairs are autosomes meaning they're not sex chromosomes one pair the 23rd pair is sex chromosomes and the sex chromosomes can either be an X or a y females are XX they get an X from their mother and an X from their father males are X Y they get an X from their mother since that's all the mother can give and they get a y from their father the Y chromosome is a real small chromosome and it mainly has genes in it that confirm maleness the X chromosome is larger and it has genes for lots of different things on it quite often um males have sex-linked chromosomal abnormalities there are diseases and disorders that are related to mutations in the X chromosome and since males only have one they have nothing to balance it out so if they have a mutation in that X chromosome they got from their mother they'll have the disease examples of that would be red green color blindness male pattern baldness certain forms of muscular dystrophy certain forms of Hemophilia they're all on the X chromosome we're both both males and females are essentially female when they're first created it's only during development when the Y chromosome the genes on the Y chromosome kick in that a guide differentiates from being a female into a male so by default we're all female at the beginning until the Y chromosome starts acting gametes are the haploid cells that's the sperm in the egg and they're going to have either an X or a y in the case of the sperm or they'll have an X in case of an egg there's a single set of chromosomes so there's only 23 and then when they come together then we'll have 23 pairs again and they're produced by meiosis so mitosis the goal there is to create two cells that are identical from one parent cell in the case of meiosis you want to produce in in the case of sperm for cells that are different from the parent cell and in meiosis in the in the case of the egg or the oocyte we want to produce one oocyte that is different from the parent cell as well so here we want to see some genetic diversity we want to see genetic recombination and we'll get into that in a little bit