Evidence for Relationships Between Organisms.

• When 1 species evolves to another species the DNA will be similar.
• Due to mutations the base sequences will change over time leading to more differences.
• Species closely related have similar DNA bases.
• DNA Hybridisation:
• Determines similarities between DNA of different organisms.
• Depends on particular property of double helix.
• DNA is heated and double strand separates, when cooled bases recombine.
• 1. DNA from 2 species extracted and cut into short species.
• 2. DNA of 1 species labelled radioactively and mixed with other DNA.
• 3. Mixture heated to separate strands.
• 4. Cooled so strands recombine with complimentary sequence of bases.
• 5. Some of reformed double strands will have 1 of each species (hybridisation).
• 6. Hybrid strands separated and temp increased in stages.
• 7. At each stage degree to which 2 strands linked is measured.
• 8. If closely related they'll share many complimentary bases so greater number of hydrogen bonds, stronger strands will require higher temperatures.

DNA Base Sequencing in Classifying Plants - DNA sequences of all 3 genes determined and compared using computer analysis. Phylogenetic tree for families of flowering plants derived.

Comparing Amino Acid Sequences in Proteins - degree of similarity in amino acids sequence of same protein in species will reflect how closely related they are.

Immunological Comparisons of Proteins:

• ABs of 1 species will respond to specific AGs on proteins in blood serum of another.
• 1. Serum albumin from species A injected into B.
• 2. B produces ABs specific to all AG sites on albumin.
• 3. Serum extracted from B (contains ABs).
• 4. Serum mixed with serum from blood of 3rd species.
• 5. ABs respond to corresponding AGs on albumin in C's serum precipitate.
• 6. > number of similar AGs, the more precipitate formed and more closely they're related.

Behaviour of members of same species more alike than members of different species so recognise members of same species. Behaviour is genetically determined, courtship and mating is essential to survival of the species. Each individual tries to ensure their DNA is passed on. It is necessary for:

• Recognising members of own species - mating only takes place between same species, to produce fertile offspring.
• Identifying mate capable of breeding - sexually mature and fertile.
• Forming a bond pair - leads to successful mating and raising of offspring.
• Synchronise mating - max possibility of sperm and egg meeting, females often only receptive to mating for short time, males use courtship behaviour to tell if female is receptive: if she responds courtship continues.

Usually males who carry out action which acts as stimulus to female who responds with own specific action = stimulus-response chain.