One of the traits Mendel studied was what makes some pea plants tall and some short. He realized that the traits must come from a factor of heredity passed from the parent plants. These factors were later called genes.
Genes are the basic unit heredity found in cells. Genes determine the physical appearance that an organism gets. For example it is the genetic information in the cells that determine your height, eye color, hair color and all the other physical characteristics a person has. A plant's height, size of its leafs and the kind of fruit it produces is all determined by its genes.
Genes are made up of segments of deoxyribonucleic acid also called DNA. They form long threadlike chains called chromosomes. The way a cells is supposed to function is all chemically encoded in the DNA.
Within a cell, chromosomes are found in matching pairs. Each chromosome has many genes, and each gene is located at a particular site on the chromosome. Genes occur in pairs.
In sexual reproduction, offspring receive one-half of their genes from each parent and the genes are mixed together. This produces new combinations of genes, so that each individual is unique but still possesses the same genes as its parents.