Our bodies are made up of patterned segments controlled by correspondingly patterned and segmented genes, or Hox genes. Changes in the number of these repeated parts (through mutations that result in gene duplication, gain of gene function, gene deletion, or loss of gene function) can perhaps explain evolutionary 'jumps" like the gain and loss of legs in various lineages (whales, snakes, legless lizards), and the addition or loss of teeth, fingers, and toes. Mutations affecting the regulation of Hox genes will also cause developmental innovations and these include changes in timing, location, and quantity of Hox gene expression.
Evolution of the vertebral column is of considerable importance to human origins. The segments of the backbone (vertebrae) have undergone changes over the course of primate evolution, most of which are attributed to changes in locomotion. Apes have six lumbar vertebrae (in the lower back) but humans normally have five. Also, both apes and humans have lost the tail all together (the very end of the vertebral column). Mutations in
Hox genes are probably responsible for these changes. --
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