genes and the environment

• discontinuous variation 


  falls in small discreet groups

  no over lapping

  represented by a bar chart

  e.g blood groups
• continuous variation 


  characteristics that are affected by genes and environment

  these are polygenic

  shown by a bell shaped curve

  e.g hair colour
• polygenic 


  controlled by a number of genes on many loci
• people can be susceptible to illness but do not have it unless triggered by the environment
• tumour suppressor 


  inhibit cell division
• proto-oncogenes 


  stimulate cell division
• in cancer the rate of cell division is faster than the rate of cell death
• a mutation in the proto-oncogene causes it to be permanently switched on even if growth factor not present

  called a oncogene

  causes uncontrollable cell growth/ tumours
• proto-oncogenes are switched on when growth factors are present on the cell membrane
• tumour suppressor gene is responsible for slowing cell division

  repairs mistakes on DNA
• less methylation causes pro-oncagenes to be permanently active so cell cycle carries on
• more methylation causes tumour suppressor genes to become inactive which causes cell cycle to carry on
• height


  better nutrition

  improved health

  better housing/ clothes
• hair colour


  lightens due to the destruction of melanin by UV light

  light increases the amount of MSH and also MSH receptors making melenocytes to become more active