Ans.Parents pass characteristics to their young through gene transmission. Equal number of chromosomes from each parent are combined during fertilization.The chromosomes carry the units of inheritance called the genes.
Genes consist of DNA. They contain specific instruction for protein synthesis. In order to know the nature and working of genes, we will have to study chromosomes in detail. The body cells have a constant number of paired chromosomes. The two chromosomes of a pair are known as homologous chromosome. In human body cells, there are 23 pairs of homologous chromosomes for a total of 46 chromosomes. We may recall that during meiosis, the two members of each chromosome pair separate and each of-them enters onegarnete.
Chromosome are made of chromatin material (simply as chromatin). Chromatin is a complex material, jnade of ONA and proteins (mainly histone proteins). DNA wraps around histone proteins and forms round structures, called nucleosomes. DNA is also present between nucleosomes. In this way, the nucleosomes and the DNA between them look like “beads on a string".The fibres consisting of nucleosomes condense into compact form and get the structure of chromosomes. Figure 15.1