A chromosome is made of two identical parts called

In many ways Gregor Mendel was quite lucky in discovering his genetic laws.  He happened to use pea plants, which happened to have a number of easily observable traits that were determined by just two alleles.  And for the traits he studied in his peas, one allele happened to be dominant for the trait & the other was a recessive form.  Things aren't always so clear-cut & "simple" in the world of genetics, but luckily for Mendel (& the science world) he happened to work with an organism whose genetic make-up was fairly clear-cut & simple.INCOMPLETE DOMINANCEIf Mendel were given a mommy black mouse & a daddy white mouse & asked what their offspring would look like, he would've said that a certain percent would be black & the others would be white.  He would never have even considered that a white mouse & a black mouse could produce a GREY mouse!  For Mendel, the phenotype of the offspring from parents with different phenotypes always resembled the phenotype of at least one of the parents.  In other words, Mendel was unaware of the phenomenon of INCOMPLETE DOMINANCE. 
 I remember Incomplete Dominance in the form of an example like so:RED Flower x WHITE Flower ---> PINK Flower With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits. 
It's like mixing paints, red + white will make pink.  Red doesn't totally block (dominate) the pink, instead there is incomplete dominance, and we end up with something in-between.