2. Fertilisation In Mammals  Sperm are produced in the testes  Eggs are produced in the ovaries  Fertilisation occurs when a sperm swims up the oviduct and fertilises an egg  The zygote develops in the uterus

3. Fertilisation In Plants  Stigma: catches pollen grains  Stamen (male part of the flower) is the anther which produces pollen grains (male gamete) and the filament  Ovary is the female part and it contains gametes called ovules

4. Fertilisation In Plants  Fertilisation occurs when a pollen grain lands on the stigma  A pollen tube grows down into the ovary  The nucleus of the pollen grain travels down the tube and fuses with an ovule in the ovary  Fusion of the two nuclei produces a zygote

5. Importance of Sexual Reproduction  Results in variety of offspring  Gametes (sex cells) are special because:  They contain only half the genetic material of all other cells  They are genetically different from one another and all other cells in the body

6. Chromosomes and DNA  Chromosomes contain genetic information that gives rise to an organisms' characteristics  Chromosomes are made of smaller segments called genes  Chromosomes (and genes) are made from DNA

7. Chromosomes and DNA  DNA is made up of lots of simpler units called bases (A, T, G, C)  Bases linked together make a genetic code (which is DNA!)  A sequence of bases makes an amino acid chain (3bases for one of 20 amino acids)  Genes on the chromosomes control what proteins are made e.g. enzymes

8. Sex Determination  Normal human body cells contain 46 chromosomes  Chromosomes exist in pairs so we have 22 pairs of body chromosomes and 1 pair of sex chromosomes  Males have an X and a Y sex chromosome  Females have two X chromosomes  Sperm cells carry either X or Y sex chromosomes so they determine the sex of the baby

9. Sex Determination

10. Meiosis  Meiosis is the process of shuffling genes and sharing out chromosomes to gametes  2 cell divisions occur  4 sex cells are produced, each having half the number of chromosomes as the parent  When gametes fuse at fertilisation, the normal number is reached again

11. Variety  Gametes are all genetically different because of the different ways that they can pair up and then divide  Sexual reproduction produces greater variety by the fusion of two gametes being a random process