According to this theory, all the cells of an individual (inclusive of the egg cells and sperm cells) have two sets of homologous chromosomes, one from the father, the other from the mother. Before the egg and sperm are ready for the production of a new individual, each loses one set of homologous chromosomes in the so-called reduction division, but the lost set is made up indiscriminately of maternal as well as paternal chromosomes, so that while one egg retains the maternal chromosome _A_ the other will retain the paternal one, and so on. If before the reduction division all the eggs had the chromosome constitution _AA₁_, _BB₁_, _CC₁_, _DD₁_ (where _A_ _B_ _C_ _D_ are the paternal and _A₁_ _B₁_ _C₁_ _D₁_ the maternal chromosomes), after the reduction division each daughter cell has a full set of four chromosomes, but maternal and paternal mixed. Thus the one cell may have _AB₁__CD₁_, the other _A₁__B₁__C₁__D₁_, etc. This, according to Sutton, is the basis of the Mendelian heredity. Suppose the determiner of a certain character (violet colour of flower in the bean) is located in a chromosome _A_ of this species. The homologous chromosome in beans with white colour may be designated as _a_. According to the chromosome theory of Mendelian heredity _a_ differs from _A_ in one point, though this difference is probably only of a chemical character and not visible. If an egg with _A_ is fertilized by a pollen with _a_ (or _vice versa_), after fertilization the chromosome constitution of the fertilized egg is _Aa_. All the other homologous chromosomes are identical and therefore need not be considered. All the nuclei of the F₁ generation have the chromosome constitution _Aa_. All will form eggs and pollen with nuclei of the same chromosome constitution _Aa_, but all these sex cells will go through the maturation division before they are fertilized; and this reduction division leads to the existence of two kinds of eggs in equal numbers, one containing only the _A_, the other only the _a_ chromosome; and the same happens in the pollen. When therefore the hybrids F₁ are mated among themselves, the following four chromosome combinations will be produced: Eggs Pollen A a A a [Transcriber's note: Diagram illustrating the four possible pairings of chromosomal characters] Possible combinations in fertilized eggs _AA_, _Aa_, _aa_, in the ratio 1:2:1. Now this is exactly the ratio of Mendelian heredity in the F₂ generation. The plant with the chromosome constitution _AA_ will form violet flowers, those with the chromosome constitution _Aa_ will form pale violet flowers, and those with the chromosome constitution _aa_ will form white flowers. To quote Sutton’s words: