Meiosis & Gametogenesis Biology Notes PDF

MEIOSIS & GAMETOGENESIS  Recombination occurs here Prophase I Thin Paired Thick Two “Moving through” -tene = thread Recombination occurs during pachytene Reduction of gene complexity is comp...

MEIOSIS & GAMETOGENESIS  Recombination occurs here Prophase I Thin Paired Thick Two “Moving through” -tene = thread Recombination occurs during pachytene Reduction of gene complexity is complete  Oogenesis During Embryogenesis Onset of Puberty If Egg is Fertilized Fertilization & Resumption of meiosis Arrest of meiosis in Prophase Resumption I of meiosis at Arrest of puberty meiosis at Metaphase II  Arrest of meiosis during prophase I Prophase I Thin Paired Thick Two “Moving through” -tene = thread Dictyate State (or dictyate resting stage) Figure 6.19 Retinoic acid (RA) determines the timing of meiosis and sexual differentiation of mammalian germ cells * *Male fate concerns meiosis only; not In males, CYP26B1 sex determination. degrades retinoic acid ADH (Active)  Retinoic Acid Signaling RANSPORT AND IMPORT RBP: Retinol binding protein TTR: transthyretin STRA6: Stimulated by RA 6 NUCLEAR RECEPTORS 1 RXR: Retinoid X Receptor 2 RAR: Retinoic Acid Receptor 3 ARE: Retinoic Acid Receptor Element RBP: Cellular Retinoid Binding Protein Figure 6.19 Retinoic acid (RA) determines the timing of meiosis and sexual differentiation of mammalian germ cells * In males, CYP26B1 degrades retinoic acid Figure 6.19 Retinoic acid (RA) determines the timing of meiosis and sexual differentiation of mammalian germ cells (Part 3) Raldh in mesonephro s Cyp26b No 1 in Cyp26b1 in gonad gonad Raldh in mesonephr os Male Femal e RA degraded in males RA not degraded in females Location of metaphase plate during oocyte meiosis leads to asymmetric cell division and polar body formation Nuclear envelope breaks down 2n 2n 2n n  Ovulation Graafian follicle Corpora Lutea (transient endocrine organ) Theca cells:Androgen hormone ____________________ Aromatase Granulosa cells: Enzyme ____________________ ketone reduction Mutations in aromatase cause virilization in XX individuals pothalamic – Pituitary – Gonadal (HPA) Axis in Fema GnRH: Gonadotropin-releasing hormone FSH and LH Ovulation Uterine Cycle Corpora lutea Estradiol, Inhibin, FSH and LH Progesterone HPA leads to two cycles in females: I. Ovarian (Ovulation) Cycle II. Uterine Cycle I. Ovulation Cycle  II. Uterine Cycle in Mammals Follicle matures Figure 6.23 The number of germ cells in the human ovary changes over the life span Why this spike in cell proliferation only to return to original number just before puberty? Hypothalamic – Pituitary – Gonadal Axis in Males GnRH: Gonadotropin-releasing hormon FSH and LH Spermatogenesis Leydig Cells Figure 7.1 Modification of a germ cell to form a mammalian sperm