Life Sciences Term 3

Evidence of evolution

• Fossil evidence: The evidence that shows characteristics that makes us similar to, or different from African apes comes largely from a study of fossils (thousands of fossil fragments)
• Genetic evidence: Scientists state that organisms are closely related and are likely to have a common ancestor if they have:
  
• Identical DNA structure
• Similar sequence of genes
• Similar portions of DNA with no functions
• Similar mutations (mitochondrial DNA)
• Species that are closely related have a greater similarity to each other than distant species
• Cultural evidence: Cultural evidence from studies of tools and weapons, as well as language is also used to show similarities and differences between humans and African apes.

Sources of variation

The genotypes and therefore phenotypes (appearance) of individuals of the same species are different from each other because:

• Crossing over in Prophase I of meiosis involves an exchange of genetic material, leading to new combinations of maternal and paternal genetic material in each new cell resulting from meiosis
  
• Random arrangement of maternal and paternal chromosomes at the equator during metaphase allows different combinations of chromosomes/chromatids to go into each new cell resulting from meiosis, making them different
  
• Random fertilisation between different egg cells and different sperm cells formed by meiosis result in offspring that are different from each other
  
• Random mating between organisms within a species leads to a different set of offspring from each mating pair
  
• A mutation changes the structure of a gene or chromosome and therefore the organism’s genotype. Since the genotype influences the phenotype, it creates organisms with new, different characteristics from one generation to the next.