BioNinja

The male and female reproductive gametes (sperm and egg) have specialised structures which reflect their functions

• The male gamete (sperm) is small and motile and only contributes the male’s haploid nucleus to the zygote

• The female gamete (egg) is large and non-motile and contributes all the organelles and cytoplasm to the zygote

Sperm:

• A typical human spermatozoa can be divided into three sections – head, mid-piece and tail
  

• The head region contains three structures – a haploid nucleus, an acrosome cap and paired centrioles
  

  • The haploid nucleus contains the paternal DNA (this will combine with maternal DNA upon fertilisation)

  • The acrosome cap contains hydrolytic enzymes which help the sperm to penetrate the egg

  • The centrioles are needed by a zygote to divide (egg cells expel their centrioles within their polar bodies)

• The mid-piece contains high numbers of mitochondria which provide the energy (ATP) needed for the tail to move
  

• The tail (flagellum) is composed of a microtubule structure called the axoneme, which bends to facilitate movement
  

Ovum (Egg):

• A typical egg cell is surrounded by two distinct layers – the zone pellucida (jelly coat) and corona radiata
  

  • The zona pellucida is a glycoprotein matrix which acts as a barrier to sperm entry

  • The corona radiata is an external layer of follicular cells which provide the egg with nourishment

• Within the egg cell are numerous cortical granules, which release their contents upon fertilisation to prevent polyspermy
  

• Although diagrams of egg cells commonly include a haploid nucleus, no nucleus will form within the egg until after fertilisation has occurred
  

  • The egg cell is arrested in metaphase II until it becomes fertilised by a sperm

Human Sperm and Egg

Human Sperm

Human Egg