sexual reproduction mammals

• what is gametogenesis?


  formation of gametes:

  • spermatogenesis - spermatozoa
  • oogenesis - ova
• spermatogenesis:


  • germ cell divides by mitosis forming spermatogonia
  • spermatogonia grows and matures to form primary spermatocyte
  • primary spermatocyte divides by meosis 1 to form secondary spermatocyte
  • secondary spermatocyte divides by meiosis 2 to form spermatids
  • differentiate and develop to form spermatozoa
  • with flagellum and acrosome.
• site of spermatogenesis?


  semi niferous tubules
• oogenesis:

  • primordial germ cell divides by mitosis and form oogonia
  • oogonia develop into primary oocyte
  • primary oocyte divides meiosis 1 to form secondary oocyte + polar body
  • secondary oocyte divides by meiosis 2 to form ovum and polar body
• why do zygotes contain more DNA from egg than sperm?

  • more cytoplasm from secondary oocyte
  • mo mitochondria
  • uneven division
• significance of meiosis?


  • half number of chromosomes - restored at fertilisation
  • genetic variation
  • via independant assortment and crossing over
• structure of ovum?


  • outer layer - follicle cells
  • zona pellucida - jelly coat, preventing polyspermy. hardens when granules release
  • haploid nucleus - restored to diploid at fertilisation
• structure of spermatozoa?


  • acrosome - containing digestive enzymes
  • flagellum
  • haploid number of chromosomes - restored to diploid
• fertilisation?


  • enzyme in acrosome digest zona pellucida (acrosome reaction)
  • sperm cell fuses with ovum membrane
  • meiosis occurs
  • cortical reaction takes place, granules release which harden zona pellucida
  • fusion between genetic material (nuclei) of sperm and ovum
  • forming diploid zygote
• embryo development?


  • zygote divides by cleavage forming morrulla
  • total mass of cells is equal to zygote
  • cells continue to divide and differentiate into blastocyst
  • blastocyst embeds into endometrium for implantation
• where does embryo receive nutrients from?

  endometrium tissue fluid
• what is a blastocyst?

  • hallow ball of cells
  • inner mass contained in one end
• advantage of large female gamete?

  provides nutrients and food storage for embryo