Definition: Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.
Input: Abstract: After fertilization, the protein products of the Drosophila homeobox gene caudal (cad) accumulate in a concentration gradient spanning the anteroposterior axis of the developing embryo. Mutations in the cad gene that reduce or eliminate the gradient cause abnormal zygotic expression of at least one segmentation gene (fushi tarazu) and alter the global body pattern.
Output:
Animal