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A student encounters an animal embryo at the eight-cell stage. The four smaller cells that comprise one hemisphere of the embryo seem to be rotated 45 degrees and lie in the grooves between larger, underlying cells (spiral cleavage).
-What does recent evidence from molecular systematics reveal about the relationship between grades and clades?
A)They are one and the same.
B)There is no relationship.
C)Some, but not all, grades reflect evolutionary relatedness.
D)Grades have their basis in, and flow from, clades.
E)Each branch point on a phylogenetic tree is associated with the evolution of a new grade.

Question

Quizplus · Accepted Answer

Recent evidence from molecular systematics suggests that some, but not all, grades (eg. spiral cleavage) may reflect evolutionary relatedness. Grades are morphological or developmental characteristics of organisms, while clades are groups of organisms that share a common ancestor. Grades can be useful in organizing and describing the diversity of life, but they may not always accurately reflect evolutionary relationships. Molecular data can provide more accurate information about the actual evolutionary relationships among organisms.

The Following Questions Are Based on the Description Below