variation and evolution

• without variation evolution could not occur
• variation means that there are differences between the members of a species
• the two causes of variation are sexual reprodcution and mutations
• sexual reproduction involves meiosis and then fertilisation
• a mutation is a change in the mount or structure of DNA
• mutagens are agents that increase the rate of mutations - x-rays and UV radiation
• there are two types of mutations gene mutations and chromosome mutations
• gene mutations occur when there is a change in a single gene eg. sickle cell anaemia
• chromosomes mutation occur when there is a change in the structure or number 1 or more chromosomes
• evolution is the genetic change that occurs in organisms over a long period of time - Charles Darwin and Alfred Russell Wallace - theory of natural selection
• observation 1 - organisms produce large numbers of offspring
• observation 2 - the number in a habitat increased until there are no longer enough resources to sustain the increase then the numbers level off
• observation 3 - there are genetic variations amongst the members of a population. These variations arise from sexual reproduction and mutations
• Deduction 1 - there is a struggle existence. This struggle is called competition. Animals compete for space, food, water and mates. Plants compete for light, space, water and minerals
• Deduction 2 - animals that are best suited for their environment survive and live on. If hey reproduce they will pass on their genes to their offspring. Those that are not well adapted will die out. This process is called natural selection or survival of the fittest.
• fossils support the theory of evolution - 1 - they can be aged, which allows them to be related to time
• fossils support the theory of evolution - changes in fossil record may be related to environmental changes
• expression is the stimulation of a cell to produce a product of a particular gene