Finally, they isolated the frog sequences that had base paired with the fruit fly homeobox DNA and determined the frog DNA sequence. ALL the animals they tested had homeobox sequences among their DNAs. Homeobox sequences found in most mammalian genes are very similar to those of Drosophila. These portions of the genes have been maintained without change throughout evolution. We call this conservation of genes .
Conservation means preserving or keeping.
Gene sequences maintained over evolutionary time are thought to be especially important, suggesting that distantly related organisms require the same or very similar genes. For example, the flour beetle and the fruit fly have a cluster of homeobox genes that are very similar, in sequence and in gene function, called the homeotic complex, or HOM-C. Genes similar in sequence and function in different organisms are called homologous genes . The insect HOM-C gene cluster is also similar to homeobox genes in mammals called Hox complexes.