Table 1

Degeneracy at different levels of biological organization

 1.  Genetic code (many different nucleotide sequences encode a polypeptide)
 2.  Protein fold (different polypeptides can fold to be structurally and functionally equivalent)
 3.  Units of transcription (degenerate initiation, termination, and splicing sites give rise to functionally equivalent mRNA molecules)
 4.  Genes (functionally equivalent alleles, duplications, paralogs, etc., all exist)
 5.  Gene regulatory sequences (there are degenerate gene elements in promoters, enhancers, silencers, etc.)
 6.  Gene control elements (degenerate sets of transcription factors can generate similar patterns of gene expression)
 7.  Posttranscriptional processing (degenerate mechanisms occur in mRNA processing, translocation, translation, and degradation)
 8.  Protein functions (overlapping binding functions and similar catalytic specificities are seen, and “moonlighting” occurs)
 9.  Metabolism (multiple, parallel biosynthetic and catabolic pathways exist)
10.  Food sources and end products (an enormous variety of diets are nutritionally equivalent)
11.  Subcellular localization (degenerate mechanisms transport cell constituents and anchor them to appropriate compartments)
12.  Subcellular organelles (there is a heterogeneous population of mitochondria, ribosomes, and other organelles in every cell)
13.  Cells within tissues (no individual differentiated cell is uniquely indispensable)
14.  Intra- and intercellular signaling (parallel and converging pathways of various hormones, growth factors, second messengers, etc., transmit degenerate signals)
15.  Pathways of organismal development (development often can occur normally in the absence of usual cells, substrates, or signaling molecules)
16.  Immune responses (populations of antibodies and other antigen-recognition molecules are degenerate)
17.  Connectivity in neural networks (there is enormous degeneracy in local circuitry, long-range connections, and neural dynamics)
18.  Mechanisms of synaptic plasticity (changes in anatomy, presynaptic, or postsynaptic properties, etc., are all degenerate)
19.  Sensory modalities (information obtained by any one modality often overlaps that obtained by others)
20.  Body movements (many different patterns of muscle contraction yield equivalent outcomes)
21.  Behavioral repertoires (many steps in stereotypic feeding, mating, or other social behaviors are either dispensable or substitutable)
22.  Interanimal communication (there are large and sometimes nearly infinite numbers of ways to transmit the same message, a situation most obvious in language)