Becuase there is a broad range of phenotypes for human height, the trait is an example of a polygenetic (poly = many, genetic = of genes) trait.
Due to the vast variations of human height, the trait is clearly not purely dominant or recessive. A dominant trait is due to a dominant allele (variation of a gene) which completely masks a recessive allele. If only dominant and recessive height phenotypes existed, there would only be two heights observed in humans!
Since there is such a vast variation amongst human heights, the trait is an example of a polygenetic trait. Polygenetic traits are traits that are influenced by more than one gene at multiple loci (locations) on one or more chromosomes. This results in a continuous distribution of traits within a species. Other examples of polygenetic traits include skin color, hair color, and weight.
Im not sure but if you think of it, the one that you didn't put any salt is a independent variable because it doesn't really rely on anything it doesn't have salt. The Dependent variable would be the 2nd and the 3rd cup because it doesn't have much salt but the 4th cup has lots of salt so its basically controlled. Hope it helps !
