Chromosomes are fine thread-like structures present in the nuclei of plant and animal cells. Chromosomes only can be seen clearly under a microscope just when a nucleus is about to divide in cell division. Chromosomes and the genes on them are composed of deoxyribonucleic acid (DNA). Chromosomes exist in pairs except in the reproductive cells. Two identical chromosomes in a pair is said to be homologous.
Genes are hereditary particles that carry the inherited characteristics of a person. Genes occur in pairs, therefore each inherited characteristic is carried by two genes. One gene from each pair comes from the father and the other from the mother. There are thousands of genes on each chromosome, all the genes in the body cells of a person are similar, but different from those in other people.
Examples of inherited characteristics carried by genes are:
(a) colour of the eyes
(b) pattern of finger prints
(c) type of hair
(d) blood group
Deoxyribonucleic Acid (DNA)
DNA is found in every living organism. in fact, it is present in every cell of the body. The DNA has all the information for creating a fully grown person with all the necessary organs and the inherited characteristics such as black curly hair and dark skin etc. All the information in the DNA is transmitted in the form of a genetic code.