Yes, DOMINANCES is a Scrabble word!

Letter values in Scrabble US: D 2, O 1, M 3, I 1, N 1, A 1, N 1, C 3, E 1, S 1.

Is it a valid word?

DOMINANCES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

superior development of one side of the body
the state that exists when one person or group has power over another
the organic phenomenon in which one of a pair of alleles present in a genotype is expressed in the phenotype and the other allele of the pair is not
the power or right to give orders or make decisions

Also: say-so.

Not playable in Scrabble US: LATERALITY, AUTHORISATION.