An individual (or subject) typically corresponds to an individual human or another organism.
A Biosample refers to a unit of biological material from which the substrate molecules (e.g. genomic DNA, RNA, proteins) for molecular analyses (e.g. sequencing, array hybridisation, mass-spectrometry) are extracted. Examples would be a tissue biopsy, a single cell from a culture for single cell genome sequencing or a protein fraction from a gradient centrifugation. Several instances (e.g. technical replicates) or types of experiments (e.g. genomic array as well as RNA-seq experiments) may refer to the same Biosample. In the context of the GA4GH metadata schema, Biosample constitutes the central reference object.
The age object permits both the (considered default) encoding of an age value in ISO8601, with arbitrary granularity; and the representation of an “age class” as qualitative ontology term. If available, a quantitative value should be used & take precedence over the age class, and class assignment should be performed at user/API level.