Difference between DNA, Gene and Chromosome

DNA vs Gene vs Chromosome

Within the cell, DNA is complexed with histone proteins called chromatin. At the time of cell division, the chromatin condensed to form chromosome.

In order to understand it clearly, Let us see how chromosomes are formed from double stranded DNA.

Level 1: Nucleotides are the building blocks of DNA. Nucleotides are joined by phosphodiester bond to form a DNA strand.

Level 2: Double stranded DNA helix is formed by the hydrogen bonding between nitrogenous bases of two strands. Double helical DNA is 2 nm or 20 A^{0 .}

Level 3: Formation of chromatin:

This DNA is wrapped around histone proteins forming “beads on a string appearance”. Each unit comprising of DNA wrapped around histone octamer (8 histones) is called nucleosome. Now the structure is called chromatin (DNA + histone protein complex). This is the 10nm chromatin fibril.

Further condensation forms 30 nm chromatin fibril followed by non condensed loop and condensed loop formation ultimately forming the metaphase chromosome of 1400nm. Maximum condensation of chromosome occurs at the metaphase stage. Therefore the term ‘chromosome’ often refers to the metaphase chromosome.

Gene

‘Gene is a segment of DNA that codes for a functional protein and RNAs like tRNA, rRNA or ribozymes’.

Gene vs Chromosome

Gene	Chromosome
Gene is a segment of DNA on the chromosome that codes for a functional protein and RNAs like tRNA, rRNA or ribozymes’.	Chromosome is the structure formed by the condensation of chromatin during cell division.
Genes basically refers to the DNA fragment that directs the synthesis of a protein.	Chromosome consists of long DNA strand wrapped around histone proteins.
Gene is segment of DNA molecule made up of nucleotides.	A mitotic chromosome consists of a centromere, pair of telomeres and an origin of replication.
The position of each gene on a chromosome is called loci.	Chromosome is a long strand of DNA containing many genes.
Gene contain coding sequence called exons and non-coding sequence called introns on the chromosome that directs synthesis of a protein.	Chromosome is a long DNA strand  containing both coding (genes) and non-coding DNA (junk DNA or spacer DNA) between genes.