Each person is Unique, but he or she also inherits some characteristic and even appearance from his or her parents. The study of how characteristic are passed on from parents to offspring is known as genetics and it affects all forms of life. At the center of the process is the deoxyribonucleic acid (DNA) molecule, which is exists  inside every living cell and contains a complex chemical code that controls way in which life forms are put together and operate. DNA is composed of genes ,and DNA ,in  turn makes up chromosomes. All of these microscopic structures living the nuclei of cells.

Genes

A gene is the basic unit of inheritance ,a small segment of a DNA molecules. There are about 100 thousands genes in the 46 human chromosomes. Genes contains the instructions to construct proteins ,which controls cell activities. Therefore Genes helps to determine the characteristic of an organism. 

DNA

A DNA  molecules contains all the information required to make and operate a specific organism. DNA is found in the nucleus of a cell and is a long structure which consists of two strands twisted together to form a double helix. The strands are linked by four chemicals called Bases ,Thymine, Adenine ,cytosine and guanine .

Genetic Code

DNA contains the instruction to make the proteins that construct the cell and control its functions. Four chemical Bases  Thymine, Adenine, Cytosine and Guanine combine in pairs to form a sequence, or code. the cell then translates this code and produces a protein. 

Genetic Engineering 

Genetic Engineering involves taking a genes from one cell and inserting them into another cell. This gives the cell new characteristic which are determined by the transferred Genes. In the future Genetic Engineering may be used on human cells, so that genetic disorders can be eliminated. 

Chromosomes

A chromosomes is a thread-like structure found in the nucleus of a cell .Chromosomes store DNA and carry DNA molecules when a cell reproduces by dividing .Most human cells contain 46 chromosomes ,divided into 23 pairs; 23 chromosomes are derived from each of the parents.

Sex Chromosome

Whether  animal is male or female is determined by one pair of chromosome called the sex chromosomes. In humans and other mammals , a female ‘s sex chromosomes are identical and are called XX. In male’s one chromosome is smaller , and the pair is called XY.

Sex Determination 

Sperm and eggs each carries one sex chromosome .Eggs carry an X chromosome and sperm carry an X or Y . When as sperm and an egg meet during fertilization , there is a 50:50 chance of producing a male XY or a female XX depending on which chromosome the sperm is carrying.