Genes.
Whether you are naturally tall or small, blond or brown haired, blue or green eyed, left or right handed; depends largely on the genes in your body cells.
A gene is a part of one of the chromosome threads inside the nucleus of each cell, those control the characteristics which are passed on from parents o their children.
When an egg is fertilized two sets of genes are put together, one set comes from the father in the sperms chromosomes and the other set from the mother in the egg´s chromosomes. Each carries half of the total instructions for the new human. Those genes passed carry instructions about body characteristics like height, hair color and eye color.
Dominant genes: the genes with ´´stronger ´´ or dominant instructions will control happens.
Heredity: is the passing on of characteristics from one generation to the next.
Chromosomes: are fine threads of material for carry instructions. There are 10.000 genes on each chromosome.
Human cells have 46 chromosomes. Sperm and eggs have only half that number. When a sperm and eggs join a new being begins to grow.


The three man stages of cells division.
First stage: Each chromosome makes an exact copy of itself.
The copies separate one chromosome from each pair goes to opposite sides of the cell.
Third stage: The cell divides. New nuclei form. Each daughter cell has the same chromosomes as the parent.