Fig 1-1.2: Organization of genes in DNA of a chromosome

1-1.3 Genome:

Genome is the complete set of genetic information of a cell or an organism; in particular, the complete sequence of DNA/RNA that carries this information. In diploid organisms, it refers to the haploid set of chromosomes present in a cell. Depending on its localization, genome may be nuclear or organellar. Organellar genomes are again of two types: mitochondrial and chloroplast genome. Genome size of organisms differs significantly between different species. The size of the genome governs the size and complexity of an organism. However, many small sized organisms, in fact have bigger genomes than their larger counterparts.

Various organisms have different sized genome as can be seen in the table below.

Species	Organism	Genome Size (Mb)
Triticum aestivum	Plant	16000
Homo sapiens	Mammal	3200
Arabidopsis thaliana	Plant	125
Drosophila melanogaster	Insect	180
Caenorhabditis elegans	Nematode worm	97
Saccharomyces cerevisiae	Yeast	12.1
Escherichia coli	Bacterium	4.64
Haemophilus influenzae	Bacterium	1.83
Mycoplasma genitalium	Bacterium	0.58