MANY ORGANISMS HAVE SIMILAR SETS OF HOMEOTIC GENES
Researchers were curious to know whether organisms other than fruit flies also had homeotic genes that regulated body patterning. Several research groups, led by Bill McGinnis, Michael Levine and Walter Gehring, examined this question.
First, they looked through the DNA from a variety of animals for sequences similar to the homeobox. They took advantage of the fact that DNA is double stranded, meaning that DNA is composed of two separable strands, connected by A-T and C-G base pairs.
How did they do this?
The two strands in DNA can be melted apart at high temperatures. Once separated, the strands are free to pair with other DNA molecules in the same mixture. If the two original strands are the only molecules in the mixture, then they will re-pair with each other, reforming the original double-stranded DNA molecule. If other DNA molecules with similar sequences are present in the mixture, then new double-stranded DNA molecules will be formed using different combinations of single strands.
To see whether other animals contain homeobox sequences in their DNA, the researchers mixed fruit fly homeobox DNA sequences with DNA from other animals, such as frogs. They heated the mixture to separate the DNA strands, then allowed the mixture to cool slowly. The slow cooling process allows DNA molecules with complementary sequences to find each other and pair together. Then they observed whether double stranded DNA sequences had formed between the fruit fly and frog DNA. Finally, they isolated the frog sequences that had base paired with the fruit fly homeobox DNA and determined the frog DNA sequence.
What did they find?
Every animal tested had homeobox sequences in its DNA.
Homeobox sequences found in most mammalian genes are very similar to those in fruit flies. These sequences have been conserved throughout evolution without much change.
Gene sequences maintained over evolutionary time are thought to be especially important to the basic development of even distantly related organisms. For example, flour beetles and fruit flies share a cluster of homeobox genes, called the homeotic complex or HOM-C, that are very similar in sequence and function.
Genes in different organisms that share similar sequence and function are called homologous. The insect HOM-C gene cluster also shares homology with Hox gene complexes in mammals.