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REPRODUCTION 6.6, 11.4, D5 Reproduction You must name and know the function of these organs The Y-chromosome In human embryos, the SRY gene (sex determining region Y) encodes a unique transcription factor that activates a testisforming pathway around Week 7 of development SRY gene • Cytogenetic Location: Yp11.2 • Codes for a transcription factor which ‘turns on’ genes to code for primary male characteristics – testes – (testosterone production) • Gene is switched on at w6 – 8 of embryo development and STOPS default development of a female embryo while promoting male development Testosterone • Essential for prenatal development into male • Stimulates interstitial cells of the testes to make sperm • Stimulates the prostate gland to make seminal fluid Romantic relationships and testosterone… According to wikipedia… • Falling in love lowers testosterone production in men but increases it in women • Testosterone ‘returns to normal’ after the honeymoon period • Fatherhood decreases testosterone production • ‘competition’ affects testosterone levels Spermatogenesis – let’s make some babymakers…. ..involves mitosis, meiosis and differentiation… Single sperm Digital artwork of a sperm, showing the head, midpiece and tail. The head of the sperm is surrounded by an acrosome ‘cap’ (blue), which contains enzymes that help the sperm penetrate the outer membrane of the egg to permit fertilisation. The midpiece contains large coiled a mitochondrion (gold) to provide energy to the tail, and two centrioloes (green), which are required for a viable embryo. Credit: Anna Tanczos, Wellcome Images BIGPICTUREEDUCATION.COM • The testes are composed of seminiferous tubules which produce sperm • Each tubule is surrounded by a basement membrane lined by germline epithelium cells • The germline epithelium will divide by mitosis to make spermatogonia (which divide by meiosis to make spermatozoa) • The developing spermatozoa are nourished by Sertoli cells • Outside of the tubules are blood capillaries and interstitial cells (Leydig cells), which produce the male sex hormone, testosterone Spermatogenesis is influenced by three hormones: LH, FSH, testosterone Section of a testis Light microscopy image of a transverse cross-section through a testis. Staining of the tissue reveals the numerous seminiferous tubules - the location of sperm production. Between them are interstitial cells that support sperm production. Credit: Spike Walker, Wellcome Images. BIGPICTUREEDUCATION.COM Seminiferous tubule Confocal microscopy image of a cross-section through a seminiferous tubule showing the developing sperm; they can be seen as a row of cells with their tails pointing into the lumen (opening) of the tubule. The nuclei are stained blue, and the mitochondria red. Sperm have a large number of mitochondria for energy to allow them to swim towards the egg. Credit: MRC NIMR, Wellcome Images BIGPICTUREEDUCATION.COM Making babymakers… • Germ cells (spermatagonia) divide by mitosis • Then there are two meiotic divisions (primary and secondary spermatocytes) to make spermatids • Spermatids differentiate into mature spermatazoa (nursed by Sertoli cells) Spermatogenesis