The B locus in dogs controls whether the dog is liver. Liver is recessive (b), so a dog needs two copies of the allele in order to be liver. If a dog is bb on the B locus then any and all black in its coat will become a brownish colour. Bb and BB have no effect.
Micro: Mini, small, tiny. Micro is also a term used in the RTS Starcraft, as a term for modified unit control. Micro can also refer to the descriptions of micro-organisms. Micro as a unit of measurement is defined as: One millionth..
The smallest unit for a living thing is a cell, and all living things are made of one or more cells. Living things also evolve with time. Broader definitions of life include things that do not have a metabolism such as virus and other self-replicating molecules.  This means that something like a bacterium is alive, while a virus  is not because it has no homeostasis mechanisms, cannot grow and it  cannot reproduce without hijacking the replicatory equipment of a  living organism.