Back
Home
8.4 discuss the evidence available from current research about the evolution of genes and their actions
discuss the evidence available from current research about the evolution of genes and their actions
- Homologues, homeotic or Hox genes are found in most or all groups of multicellular animals and show similar DNA sequences suggesting that these genes evolved in a common ancestor. These genes, being similar in both structure and function, are expressed in similar sequences on chromosomes.
- The study of DNA sequences provides evidence for the evolution of genes. Sequences of bases in genes that do not change or change very slowly over time are used to measure relationships between groups of organisms. For example, in mice, the gene for the development of eyes is similar to the gene in insects.
- Previously, amino acid sequences in proteins such as haemoglobin, have been used to determine evolutionary relationships. The protein myoglobin in insects provides oxygen to cells and is very similar to a protein with a similar function in primitive fish. Studies of all of these proteins responsible for carrying oxygen suggest an evolutionary pattern for their development. The analysis of the DNA that makes up the genes that code for proteins has provided more evidence of evolutionary changes in certain groups of organisms.
- The study of mutations of homeotic genes shows that a small mutation can suddenly affect an organism as a gene cascade is altered. A mutation in a homeotic gene can cause one part of the body to develop into another. For example, in Drosophila fruit flies, one mutation in a homologue gene can result in legs growing on the head rather than antennae. In humans, a mutation in a homeotic gene for the development of the bones of the skull results in rigidity in the joints between these bones. This can result in abnormal brain growth and possible mental retardation. The base sequence for this gene is very similar in many animals.
- These gene changes can then result in often dramatic alterations in organisms which may then lead to the rapid evolution of new body structures. This is evidence for the expansion of diversity of living things and the theory of punctuated evolution.