n, pl  -gies  1 a  :  likeness in structure between parts of different organisms due to evolutionary differentiation from the same or a corresponding part of a remote ancestor - compare ANALOGY HOMOMORPHY   b  :  correspondence in structure between different parts of the same individual  2 a  :  the relation existing between chemical compounds in a series whose successive members have in composition a regular difference esp. of one carbon and two hydrogen atoms CH₂  b  :  the relation existing among elements in the same group of the periodic table  c  :  similarity of nucleotide or amino acid sequence in nucleic acids, peptides, or proteins .
 
   
 
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