الفهرس 
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Abstract
The higher animals originate from the union of two gametes, the ovum and the spermatozoon. These cells contain all that the new individual inherited originally from his or her parents. The bearers of the hereditary elements, the genes are identified as either, structural genes (which code for structural proteins such as enzymes, hormones or haemoglobin) or central genes to accelerate or decelerate translation processes of other structural genes (Renie, 1986).
The genes are present in the cell nucleus in the form of chromosomes, which are no more than the chromatin granules seen in the nuclei of cells during the interphase stage of the cell cycle. These granules are found to be composed of, DNA (Desoxyribonucleic acid), histone and non histone proteins (Swanson et al., 1981).
Roberts (1974) mentioned that each long strand of DNA is formed of two strands helically arranged. Each strand is composed of pentose sugar (deoxyribose), phosphate and protein bases which are two pyrimidine bases; cytosine (C) and thymine (T) and two purine bases; adenine (A) and guanine (G). The sugar and phosphate components are constant but purine and pyrimidine bases confer individuality. The two strands of sugar and phosphate components are linked by pairs of bases. The base pairs are of four kinds only, AT, TA, CG & GC. Adenine paired with thymine and cytosine paired with guanine. The two bases of each pair were linked by hydrogen bond.
Nowel (1960), observed that the chromosomes at the metaphase stage of the cell cycle can be conveniently seen and appear to be relatively short and thick. This is because they are tightly coiled like spiral springs. Hence, the chromosomes can be seen to compose of two identical strands, sister chromatids joined at the centromere. He also stated that the chromosomes are in fact, long fine filaments and they bear a very large number of genes.