Gametes

• Gametes are the?sex cells?of an organism
  • For example, the?sperm?and?egg?(ovum) cells in humans
• Gametes fuse during fertilisation to form a?zygote
  • Fertilisation is the?fusion of the nuclei?from a?male gamete?(sperm cell) and a?female gamete?(egg cell)
• These sex cells are formed during?meiosis?and only have?one copy of each chromosome, so they are?haploid?cells
  • For humans, that means the sperm and egg cells contain 23 single chromosomes in their nucleus

Sexual reproduction involves the fusing of two gametes to form a zygote that contains DNA from both parents

Mammalian gametes are specialised for their functions

• Mammalian gametes have?adaptations?to?increase the chances of fertilisation?and?successful development of an embryo
• Sperm cells:
  • Have a?flagellum?(tail) that allows them to?swim?towards the egg cell
  • Contain?many mitochondria?that?provide energy for movement?of the flagellum (swimming)
  • An?acrosome?that contains?digestive enzymes?to break down the protective glycoprotein layer (a jelly-like coating known as the?zona pellucida) surrounding the egg cell - sperm cells must penetrate this layer in order to fertilise the egg
• Egg cells:
  • Are?much larger?than sperm cells as most of their internal space contains?food to nourish a growing embryo
  • Have follicle cells that form a protective coating
  • Have a jelly-like glycoprotein layer, known as the?zona pellucida, that?forms an impenetrable barrier after fertilisation?by a sperm cell has occurred, to?prevent other sperm nuclei from entering the egg
• These features are summarised in the diagrams and tables below

Structure of a mammalian sperm cell

Structure of a mammalian egg cell

Adaptations of Mammalian Gametes Table