B5.2 natural selection

• intraspecific variation


  variation within populations
• mutations are 


  rare and random changes that occur in the sequence of DNA bases in a gene or a chromosome
• causes of mutations

  1. gamma rays, x-rays and ultraviolet rays - all types of ionising radiation can damage bonds and cause changes in base sequences
  2. certain types of chemicals
• natural selection process:

  1. variation exists in a species, which is caused by a variety of alleles formed by mutation
  2. organisms reproduce - more than is suitable for the environment
  3. competition between individuals for resources
  4. individuals with more advantageous characteristics for the environment will survive and reproduce
  5. alleles resulting in higher survival rates are passed onto offspring at a higher rate
  6. in the next generation, more individuals have the advantageous variation
• evolution

  the change in adaptive features of a population over time as a result of natural selection
• how are fossils formed?

  1. reptile dies and falls ground
  2. flesh rots, leaving skeleton to be covered in soil / clay before it is damaged
  3. protected over millions of years, the skeleton becomes mineralised and turns to rock.
  4. the rocks shift in the earth with the fossil trapped inside
  5. eventually, the fossil emerges as the rocks move and erosion takes place
• how does extinction prove evolution?

  species that cant adapt to environmental changes die out.
• why do scientists classify organisms?

  to identify species

  to predict characteristics

  to find or show evolutionary links