Mendel also described how genes from one generation are passed on to the next generation. When an organism reproduces, one copy of each of its genes is randomly chosen for inclusion in its sex cells (egg and sperm); this is now termed the Law of Segregation. He also noted that each observable trait was independently passed down from other traits, this phenomenon is referred to as the Law of Independent Assortment. For example, the smoothness of the seed shape was transmitted independently from the color of the flower. Each observable trait could be traced back to a single gene. These rules became known as Mendelian genetics.
While Mendelian genetic rules apply to many phenotypes, we now know that these rules are too simplistic to predict some traits. Some traits are coded by more than one gene. Furthermore, some alleles are co-expressed such as red flowers crossed with white flowers to produce pink flowers. This is also seen with human blood typing. A and B blood types are co-dominant alleles.
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