<em>The genotype of an organism determines its phenotype</em>. Phenotype is constituted by observable characteristics of an organism. These characteristics are codified by genes, and the combination of the differents variants of a gene which codify a phenotipic characteristic constitutes the genotype. For example: eyes color is a characteristic. Its is codified by variants of a gene. The combination of two variants of a gene gives a genotype, which codifies for the phenotype 'blue eyes'.
Blood is pushed through the organism by the heart, and brings nutrients and oxygen to our tissues. It also takes away waste and carbon dioxide from tissues.
