Forelimbs form at the junction of the neck and thoracic vertebrae, the position of which is controlled by HoxC-6 genes. Several kinds of vertebrates from different Classes are legless, including legless lizards, and amphibians known as caecilians. All descended from legged forms. On the basis of recent research in genetics what would you predict about the functioning of their HoxC-6 genes?
A. The site of expression of their HoxC-6 genes may have moved anteriorly until the level of expression has eliminated the neck region.
B. The site of expression of their HoxC-6 genes would be the same as that of legged vertebrates but is simply turned off early in development.
C. Their HoxC-6 gene has mutated and serves a different function than in legged vertebrates.
D. The effect of the HoxC-6 gene is masked by another gene that is dominant to it.
E. None of the other choices provided offer an adequate explanation and other reasons must be sought.
A. The site of expression of their HoxC-6 genes may have moved anteriorly until the level of expression has eliminated the neck region.
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