Variation with a Species (Edexcel IGCSE Biology: Double Science)

• Variation is defined as differences between individuals of the same species
• Variation can be caused by:
  • differences in genes brought about by random fertilisation of gametes
  • environmental factors
  • a combination of both

Environmental Variation

• Characteristics of all species can be affected by environmental factors such as climate, diet, accidents, culture and lifestyle
• In this instance ‘environmental’ simply means ‘outside of the organism’ and so can include factors like climate, diet, culture, lifestyle and accidents during lifetime
• Examples include:
  • an accident may lead to scarring on the body
  • eating too much and not leading an active lifestyle will cause weight gain
  • being raised in a certain country will cause you to speak a certain language with a certain accent
  • a plant in the shade of a big tree will grow taller to reach more light

Genetic and Environmental Causes

• Discontinuous variation is usually caused by genetic variation alone
• Continuous features often vary because of a combination of genetic and environmental causes, for example:
  • tall parents will pass genes to their children for height
  • their children have the genetic potential to also be tall
  • however if their diet is poor then they will not grow very well
  • therefore their environment also has an impact on their height
• Another way of looking at this is that although genes decide what characteristics we inherit, the surrounding environment will affect how these inherited characteristics develop