The neural crest and gene duplication. From Urochordates Segments form first under the control of segmentation genes. Gene duplication can contribute to increased complexity. Evidence that homeotic loci are the result of gene duplication. Finally in the mouse, there are 4 sets, not just one.
Genes lie in sequence on the chromosome which indicates side by side duplication.
Same alignment in the groups of loci found on different chromosomes in the mouse. In the mouse, the similarity is greater between loci in the same position on different chromosomes than different position on the same chromosome. Same regulatory type of protein active during the same stage in development. Now the hypothesis for the duplication of the homeotic genes and the complexity of vertebrates. Amphioxus one set in a simple bilateral organism no back bone and no jaw 2.