A genome is the genetic material of an organism which consists of DNA or RNA). The genome includes both the genes (the coding and noncoding DNA) like mitochondrial and chloroplast DNA. The study of the genome is called genomics.

A genome sequence has a list of nucleotides contain (A, C, G, and T for DNA genomes) that make all the chromosomes of both of an individual or a species. Inside a species, the majority of nucleotides are identical between individuals, but the sequencing is necessary to understand the genetic variety.

Types of Genome
Viral genomes
Prokaryotic genomes
Eukaryotic genomes

Viral genomes

Viral genomes are composed of either (DNA or RNA). The genomes of RNA viruses and DNA viruses can be either single or double-stranded RNA, While DNA viruses can have either single or double-stranded genomes.

RNA viruses may contain one or more separate RNA molecules and DNA virus genomes contain a single, linear molecule of DNA, in which some are made up of a circular DNA molecule.

Prokaryotic genomes

Prokaryotes and eukaryotes both have DNA genomes. Archaea have a single circular chromosome like most of the bacteria, Prokaryotic contain single chromosome and Eukaryotic contains multiple chromosomes.

Some bacteria have auxiliary genetic material, which is carried in plasmids.

Eukaryotic genomes

Eukaryotic genomes are composed of one or more linear DNA chromosomes as we mentioned before.

The number of chromosomes varies from jumper ants to an asexual nematode, which each have only one pair in a fern, species has 720 pairs.

A typical human cell has two copies of each of 22 chromosomes, one from each parent, and two sex chromosomes which make it diploid.

It means human cell contain 46 chromosomes 23 from each parent, transfer characteristics to child. Change in the number of chromosomes may occur abnormality in the human body.

For example, gametes such as (ova, sperm, spores, and pollen) are haploid, it means they carry only one copy of each chromosome.

In addition to the chromosomes in the nucleus, organelles such as the (chloroplasts and mitochondria) have their own DNA. Mitochondria have their own genome named as "mitochondrial genome".

Unlike prokaryotes, eukaryotes have protein-coding genes and variable amounts of repetitive DNA. In mammals and plants, the majority of the genome is composed of repetitive DNA.

Composition of the human genome
Coding sequence
Noncoding sequences

Coding sequence

DNA sequences carry the instructions to make proteins. In plants and amphibians, the proportion of repetitive DNA is more than 80%, while in the human genome codes for proteins are 2%.

Noncoding sequences

Noncoding sequences include introns. Noncoding sequences make 98% of the human genome. Tandem repeats and Interspersed repeats are two categories of repetitive DNA in the genome.