Gene vs Genome
Each species has a unique set of inherited characteristics that make them different from each other species. Usually these characteristics are encoded in the DNA (deoxyribonucleic acid) molecules present in their cells. Gene properties and genome properties vary widely from one species to another. Gene and genome, both terms are associated with DNA and both terms are defined by using DNA molecule. DNA is the basic unit of heredity which is mainly found on chromosomes within the nucleus of cells or within other organelles.
What is Genome?
In general, the total DNA content in a single cell is known as the ‘genome’ of the organism. This is true for many organisms, but in some viruses, they have only RNA so that their genome is the total quantity of RNA content. In modern molecular biology, genome is the entire quantity of heredity information, thus includes both genes and the non-coding sequences of DNA/RNA. The term ‘genome’ can also be applied to refer to specific genetic contents. For example, the total content of the nuclear DNA in a cell is called ‘nuclear genome’ and the total DNA content in mitochondria is called ‘mitochondrial genome’. In addition, genome may also comprise of non-chromosomal genetic elements such as viruses, plasmids and transposable elements.
The study of genome properties of related organisms is called genomics. Evolution of genome can be identified with the help of genome composition, which includes genome size and proportions of non repetitive and repetitive DNA. If we consider the human genome, it contains 23 chromosomes. Out of 23, only one chromosome is a sex determinative while the remaining 22 chromosomes are autosomal chromosomes. There are approximately 20,000 to 25,000 genes of the human genome. To identify and map the sequence of chemical base pairs which make up the human DNA, there is an international project going on since 1990 called ‘The Human Genome Project’.
What is a Gene?
Genes are the elements of heredity that determine the inherited genes which are transmitted from parents to offspring in reproduction. The existence of genes and their transmitting processes were first suggested by Gregor Mendel. He called genes as ‘factors’ and found that most heredity elements are transmitted from parents to offspring. However, Mendel did not know about the DNA. Later scientists discovered the DNA as the main genetic material found in organisms.
Genes are composed of specific DNA portions or segments. These specific segments are capable of controlling specific heredity characteristics. This is usually done by DNA transcription and DNA translation processes. In sexual reproduction, offspring obtain one gene of each type from both parents. The different forms of a gene are known as alleles. A single allele, or several alleles are responsible for controlling certain characteristics in the organisms.
What is the difference between Gene and Genome?
• Gene is a segment or a portion of DNA molecule while genome is the total DNA content in a cell.
• Genes code for proteins. Genome itself cannot code for proteins as it contains almost all the DNA. Since the gene is only a portion of a DNA molecule, that part is enough to code for proteins. This results in a vast variation of protein molecules in an organism.
• Genome consists of all the base pairs in a cell. Gene consists of only a few base pairs as it represents only a DNA segment.
• The study of properties of genes is referred to as ‘genetics’ while the study of properties of the genome is referred to as ‘genomics’.
• In general, an organism has one genome, but it has thousands of millions of genes in that particular organism.
Suhardi, Ph.D 