Echinoderm microfossil dating

The term refers to a spatial gradient in any measurable characteristic—for example, allele frequency or the mean of a quantitative trait.Subdivision of molecules, cells, or genetic functions into discrete spatial or temporal units.

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Common structural motif of proteins in which linear amino acid sequences (“strands”) located in different regions of the polypeptide chain align adjacent to each other and are stabilized by hydrogen bonding between backbone atoms located in different strands.All chordates contain a solid rod, called a notochord, along the length of the body during embryogenesis and a dorsal nerve cord and pharyngeal pouches.A smooth change from place to place across a spatially continuous habitat.Member of a major subdivision within the protostomes that includes the arthropods, nematodes, and several smaller phyla.Members of this group possess an external covering called a cuticle that molts as the animal grows.