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8.3 describe the evidence which indicates the presence of ancestral vertebrate homologues in lower animal classes
describe the evidence which indicates the presence of ancestral vertebrate homologues in lower animal classes
- Homologous structures such as pentadactyl limbs in vertebrates provide evidence for evolution from common ancestors. In a similar way, there are DNA sequences that are similar in many organisms. These DNA sequences are called homologue genes, homeobox or Hox genes. These genes regulate the development of an organism by producing proteins that switch other genes on and off.
- An example of a homologue is the gene cascade for skeletal and neurological development in limbs. It is similar in organisms such as humans, chickens, rodents, insects, nematodes and molluscs. Experiments have confirmed that the homologue gene from an amphibian can regulate the corresponding gene in mammals. A mammal homologue gene can regulate the corresponding gene in insects such as fruit flies.
- These homologue genes exist in many eukaryotic organisms, both vertebrates and invertebrates as well as some fungi and plants. This suggests common ancestry between all eukaryotic organisms.
Additional information
Evidence from biochemistry and molecular biology shows that all cells contain similar amino acids, nucleotides, sugars and fatty acids. Chemical processes such as protein synthesis within cells are also similar. Palaeontology and comparative embryology have revealed similar processes involving homologue genes in the development of the bones of the head, dentition, brain and limbs. Genes for repairing DNA are similar in all eukaryotic organisms. Photosynthesis, like all chemical reactions is controlled by a protein found in chloroplasts. This protein is similar in all plant species as well as some cyanobacteria.