Genes and Chromosomes

Eukariotic cell nuclei contain chromosomes - the contiguous structures in which DNA is stored. Every somatic cell usually includes two copies of each chromosome (excluding the sex X,Y chromosomes). The number of chromosomes varies among species. Humans have 22 pairs of chromosomes, plus the sex chromosomes.
A gene is a specific sequence of nucleotide bases along a chromosome carrying information for constructing a protein. Genes are parts of the cromosomes. In humans genes constitute approximately $5-10\%$ of the DNA, leaving $90-95\%$ of noncoding "junk DNA". The role of the latter is as yet unknown, but it is speculated that it plays a very important role. Certain theories have been suggested, such as physically fixing the DNA in its compressed position, preserving old genetic data, etc.