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| Modern Genetic Analysis Chapter 16. The Genetic Basis of Development The Many Parallels in Vertebrate and Insect Pattern Formation Genetics In Process 16-5: Finding cognates of Drosophila developmental genes With the discovery that there were numerous homeobox genes within the Drosophila genome, similarities among the DNA sequences of these genes could be exploited in treasure hunts for other members of the homeotic gene family. These hunts depend on DNA base-pair complementarity. For this purpose, DNA hybridizations were carried out under moderate stringency conditions, in which some mismatch of bases between the hybridizing strands could occur without disrupting the proper hydrogen bonding of nearby base pairs. Some of these treasure hunts were carried out in the Drosophila genome itself, looking for more family members. Others searched for homeobox genes in other animals, by means of zoo blots (Southern blots of restriction-enzyme-digested DNA from different animals), by using radioactive Drosophila homeobox DNA as the probe. This approach has led to the discovery of homologous homeobox sequences in many different animals, including humans and mice. (Indeed, it is a very powerful approach to go "fishing" for relatives of almost any gene in your favorite organism.) Some of these mammalian homeobox genes are very similar in sequence to the Drosophila genes.

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