Chromosomes are thread-like structures located inside the nucleus of cells. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
see the picture which illustrate that also show the true genetic content & non genetic areas....
Promoters: are DNA sequences adjacent to the beginning of the genes and control gene activation.
Introns are sequences inside the gene although they do not code for protein sequence they are necessary for correct coding.
Exons are the regions inside the gene between introns that contain the coding DNA sequences.
Most of the harmful mutations occur in exons and as a consequence change the structure of the coded protein.
