why does a child tend to resemble one parent or the other rather than being a blend of the two?
Actually, a child is exactly a blend of the DNA of both parents. However, some genes are dominant and others are recessive. The dominant genes are the ones that will be displayed more often than the recessive ones in the offspring's phenotype. That is because only one copy of a dominant gene is necessary for its expression. In order for a recessive trait to be seen in the offspring, each parent has to contribute a recessive gene to the offspring. In other words, two recessive genes are needed in order to be seen in the phenotype of the offspring. In sexually reproducing organisms, the offspring has 50 percent of its DNA from the mother and 50 percent from the father. However, the dominant traits are the ones we see most often in the offspring.