Early embryonic development (metaphase in mitosis) over time, from upper left to lower right with tubulin (microtubules) labeled, showing the elongation of the mitotic spindle prior to the first cell division. Courtesy of Ahna Skop, Skop Lab.
Similarity in the sequence of a protein or nucleic acid or in the structure of an organ that reflects a common evolutionary origin. Molecules or sequences that exhibit homology are referred to as homologs. In contrast, analogy is a similarity in structure or function that does not reflect a common evolutionary origin.