Explain the genetic evidence for the evolutionary changes that caused the loss of forelimbs in snakes
What will be an ideal response?
ANSWER: Most snakes lack limbs. However, they have Hoxc6 and Hoxc8 genes that are associated with
the formation of limb buds and forelimbs in other vertebrates. In these animals, ribs, but not
forelimbs, grow where both Hoxc6 and Hoxc8 genes are expressed. In snakes, these genes are
expressed all along the backbone, beginning at the base of the skull; therefore, the ribcage
develops just behind the head and limbs and limb buds do not form. This spatial patterns of
gene expression caused the loss of forelimbs in snakes.
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Well-designed microbial activity measurements can reveal ________ of major metabolic reactions in a habitat
A) types B) rates C) both types and rates D) either types or rates (but not both)
Mutant forms of proto-oncogenes are called ____________________
Fill in the blank(s) with correct word
A tracheid is
A. a gametophyte cell. B. a small branch of an insect trachea. C. a seed-bearing stem. D. a specialized vascular cell. E. a reproductive chamber.