How Heredity Works

  Cells grow. When they reach a certain size, they divide into two new cells. It exists two types of cells mitosis and meiosis. Mitosis is a continuos process. Mitosis occurs in all the body except in the sex cells and Meiosis is the division of the nucleus resulting in sex cells.

When an organism reproduces, a sperm cell from the male parent fertilizes with, an egg cell from the female parent. It received half of the needed chromosomes of the male and the female parent cells. The fertilized egg will now develop as the parent's offspring.

Gregor Mendel realized that all organisms get two copies of each factor. Today scientist called this factors genes. A gene is the portion of a chromosome that controls a particular trait. It contain the information needed cells to function.
Genes are portion of long,complex molecule called deoxyribonucleic acid, or DNA. DNA containd the codes that tell each cell to operate. The genetics charasteristic of every living organism are contained in the DNA. The codes of the DNA molecule contains related to the molecule's structure. The shape looks like a spiral staircase. The steps of the staircase are made of chemical compounds , called bases, that fit together like the pieces in a puzzle.The four DNA are cytosine (C), guanine(G), thymine(T) and adedine(A). The order allows for huge numbers of combination. 
During mitosis the cell produces a second chromosome. To copy each chromosome , the cell must take a second DNA molecule with exactly the same order of base pairs as the original.