Biochemical evidence for evolutionary relationships

This section focuses on observing differences examined biochemically to determine evolutionary relationships.

Comparison of proteins

Species that are closely related are expected to have fewer differences in amino acid sequences of particular proteins than species that are distantly related. The longer periods of divergence the more likely that there will be changes in amino acids sequences.

Comparison of DNA sequences

By comparing DNA sequences through sequencing we should be able to determine evolutionary relationships. If evolution has occurred then the genes present in an ancestral species will also be present in members of a related group due to conservation. This does not mean the sequences will be identical, but they will be fairly similar.

DNA can also be compared on the basis of chromosomes through looking at banding patterns and through the use of chromosomal painting (which involves the use of probes that can be applied to chromosomes of other species)

DNA hybirdisation

DNA hybirdisation provides evidence on the relatedness between two species.

DNA hybridization requires DNA to be removed from two species to be compared which are separated by heat, to allow separation.

Separated strands area allowed to pair between the species and the degree of pairing (hybridization) depends on the relationships between species.

The closer related the greater the pairing.

Mitochondrial DNA (mtDNA)

  • Mitochondria have small, circular molecules of double stranded DNA.
  • It evolves relatively quickly so it is useful in determining animals that have diverged from one another in a relatively short time (20 million years).
  • Mitochondrial DNA is passed on maternally so it is identical and very little change occurs through generations. The lineage can be traced through sequencing the hypervariable regions of the mtDNA.
  • Mutation rate is easily measured in mitochodrial DNA for tracking materilineage. Sperm cannot be used as the sperm are usually destroyed by the egg cell after fertilization.
  • The degree of relatedness, is based on observing the similarities in the mtDNA.

See also