The evolution of the vertebrate has produced a diversity of body designs (see Fr

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The evolution of the vertebrate has produced a diversity of body designs (see Freeman and Herron 2007). Haxc8 (one of the box genes) determines the development of the thoracic region of vertebrates such as the mouse and chicken (Belting et al 1998). Haxc8 affects the development of the thoracic vertebrae (with ribs), paraxial mesoderm, neural tube and spinal nerves Belting et al (1998) demonstrate how a modification in an enhancer in Hoxo8 can shift the development from the seven cervical vertebrae of a mouse to 14 cervical vertebrae of a chicken. The chicken also has fewer thoracic vertebrae because Haxc8 gene is expressed over a smaller domain during the development of the chick embryo (Belting et al 1998). What does this suggest about the evolution of vertebrates? Explain the following based on the function of the Hoxc8 gene in development as described in Belting et al (1998). a) How could the general mammal body plan evolve from an ancestral vertebrate with more cervical vertebrae1 Assume having fewer cervical vertebrae tor more thoracic vertebrae) would be favored in mammals. b) How can the number of cervical and/or thoracic vertebrae change in a reptile by changes in Haxc8 gene? How did the Haxc8 gene change in the body design of a snake (snakes have thoracic vertebrae for most vertebrae in the body)? c) Why does the giraffe (a mammal) have only seven cervical vertebrae with its long neck? Only seven vertebrae in the neck is not the optimal solution for a long neck because of reduced flexibility of the neck. Based on what you have learned about the Haxc8 gene, does this mean that it is impossible to add cervical vertebrae or is there another possible explanation-1 Explain Literature Cited Belong, H. G., C. S Shashikant and F. H. Ruddle 1998. Modification of expression and deregulation of Hoxc8 in the evolution of diverged axial morphology Proceedings of the National Academy of Sciences USA 95:2355-2360 Freeman. S. and J. C, Horron 2007. Evolutionary Analysis 4th ed. Pearson Prentice Hall San Francisco.

Explanation / Answer

Ans.1.) The general mammal body evolved from ancestral vertebrae with more cervical vertebrae is result of incessant evolution. It is clear, when the evolutionary pattern of mammalian vertebral formulae along the phylogenetic pathways and hierarchical pattern is analyzed along with the evolution of the mammalian vertebral formulae.

2.) The number of cervical and thoracic vertebrae change in reptile by change in Hox8 Gene is continuous process of evolution. Evolution is most clearly perceived as changes in morphological features which include phylogeny and the changes are often hierarchically distributed among animals which confer the hierarchy of taxonomy. It is also reported that the somite segmentation also plays an essential role in the development of vertebrae. The disruption of some segmentation genes, for example Delta 1 and Wnt-3 triggers the homeotic transformations of vertebrae. Moreover, such transformations are always accompanied by changes in expression pattern of Hox gene which are firmly connected to the somitogenesis.

3.) In giraffe, each and every vertebra is connected by a ball-and-socket joint which gives a greater range of motion to move their neck. This is the same kind of joint that we humans have in our shoulders. The average height of Giraffes is between 14 and 17 feet tall and their neck provided approximately six feet of that height. The neck alone weighs about 600 pounds.

A long neck permits the giraffes to feed on trees that other animals cannot reach, including acacia trees that is a favorite food for giraffes. They also possess long tongue that is almost 18 inches long and allow the giraffe to reach even higher for foliage. Giraffes eat up to 75 pounds of plants and drink as much as 100 gallons of water each day.

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