User talk:Z3372824

• Some cells live just a day, liver 1 month etc. variable time • 2 copies in genome (us) crossing over occurs in gametes. Following s phase: 4 copies of every chrom. Duplication to get 2 daughter cells.

• G1- GROWING IN VOLUME. Most variable time in life. Check point: division of cell okay? Screening: bad: won’t copy genome, stops uncontrolled cell replication • G0: leaves cell cycle that cant divide again. E.g. Satellite cells (transiently there) • S Phase: (before mitosis) duplication of genome. Check point 2: copy of chromosome okay? No= stops cell dividing. If checkpoint goes bad: cancer e.g. p53. • G2: gets cell ready to divide (mitosis entry: so stock up on ATP) In mitosis no gene expression! Cant make new energy. (short prd of time) • 5 stages of mitosis: prophase, prometa, meta, ana, tela (defined by nucleus underlying mitosis) 2. Disassemble cytoskeleton. Microtubules form spindle only during mitosis: transport vesicles, nucleus) NO ROADWAY: so no exocytosis, endosytosis • Cytokinesis: division of cytoplasm. Overlaps with telophase. Microfilament (actin filaments) acts as belt, cuts into 2. • Meiosis diff to Mitosis : does it twice: but no duplication again: so get haploid. Crossing over. No duplication. Recombination occurs. Only 1 copy of every chromosome. Only in germ cells. Recomb : prophase 1. Indep assortment of chromosomes in meiosis 1. Progeny diff not identical.

• Female gametogenesis occurs in embryo. Oogenesis. Normally puberty: 12-13. All arrested at meiosis 1. Only complete meiosis 1 once oocyte released. (grafted follicle only, other follicles don’t complete it). Ovulated oocyte doesn’t complete meiosis 2 unless its fertilised. When it does, get a second polar body. Possible: 1st polar body also undergoes meiosis 2 then get 3 polar body. No point. • Meiosis 1 = major cause of Down’s. 1 chromosome gets left behind on spindle apparatus = 3 chrom 21’s. Instance increase with age. Aneuploidy= abnormal number of chrom. Meiosis safest when it occurs quickest, age increase, resources decrease. More env. exposure. • Male: diploid spermatogonia in testes. Around periphery of seminiferous tubule. Undergo mitosis before meiosis ( to replace itself coz it’s a stem cell). Setoli cells: support to spermatozoa. Its junctions form blood-testes barrier. • Primary spermatocyte : meiosis 1. Secondary spermatocute: meisos 2 ( cant see it coz it does it so quickly) Spermatid: round, haploid cell that’s completed meiosis, but hasn’t completed everything yet in development? Cytokinesis not completed! All progeny joing by cyto bridges? UNLIKE FEMALE 2 with x chromosomes, 2 with y. • Oocyte takes years, male takes 44 days? • Cortex thicker in infant (only primordial follicles), than older. Get germinal epithelium then cortex then medulla? Stromal cells (tiny dots?) • Medulla: large maternal blood vessels. Not many primordial oocyes here. • HUGEEE variability in number of NGF’S (oocytes) lose it by apoptosis (atresia) • Ovary lies within peritoneal cavity. Oocyte increases in volume, 4 hormones released.