sexual reproduction

• Gametes are the sperm cells in males and egg cells in females. In sexual reproduction two gametes join together at fertilisation to form a zygote, which divides and develops into a new organism.
• Normal body cells have the diploid number (2) of chromosomes - meaning each cell contains two of each chromosome (a pair), one from the mam and one from the dad. The chromosomes that make up each pair are the same size and have the same genes, although they could have different versions of those genes (called alleles). These pairs of matching chromosomes are called homologous chromosomes.
• • Gametes have a haploid (n) number of chromosomes - there's only one copy of each chromosome.
  • At fertilisation, a haploid sperm fuses with a haploid egg, making a cell with the normal diploid number of chromosomes.
  • Half these chromosomes are from the father (the sperm) and half are from the mother (the egg).
  • The diploid cell produced by fertilisation is called a zygote.