Difference between Gene and Allele

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Gene

Gene is the portion of the genetic code listed in DNA [Deoxyribonucleic Acid], which is responsible for a particular character in an organism. Genes occurs in pairs, one portion coming from mummy and another from daddy.

Allele

Allele is a particular instance (value) of the gene. Allele may also be thought of as a version of the gene. An example: Let say the gene for ‘height’ of an individual is denoted by H. The possible values for (H) are ‘tall (H)’ or ‘dwarf (h)’.

Difference Chart between Gene and Allele

Gene Allele Remarks
Definition A section of DNA coding Allele is a particular instance (value) of the gene.
Dominance n / a Dominant, Co-Dominant,
Incomplete Dominant, Recessive.
Expresses Gene cannot express; Allele can however, express Yes, if Dominant #
Examples Height Tall (H) Dominant Allele
Dwarf (h) Recessive Allele
Blood group IA Co-Dominant
IB Co-Dominant
i Recessive
Analogy A variable named 'xyz' Value of 'xyz' like 1.23 or 14.56
(#) - recessive allele expresses only in homozygous condition

Function

Gene is a section of genetic code in DNA, responsible for a particular trait in an organism. This code is then copied to mRNA (messenger RNA) by a process called 'Transcription'. This mRNA then leaves the nucleus of the cell and goes to ribosome, where it synthesizes a polypeptide chain - the building block of 'Protein'. This synthesized protein then expresses as a particular trait (like eye-color or height or blood type). Genes are always in pairs: one from mother and another from father.


An Allele is a particular version (variation) of that gene. An allele may be dominant or recessive, or co-dominant or show incomplete dominance. A gene may have many alleles (case of multiple alleles eg. ABO blood group allele). If the allele of a gene from father is same as that from mother, this condition is called 'Homozygous' condition; if different, then the condition is called 'Heterozygous'

A dominant allele expresses (synthesizes the protein) irrespective of the fact that it occurs in homozygous or heterozygous condition, while suppressing the expression of recessive allele.

A recessive allele expresses only if it occurs in homozygous condition.

A co-dominant allele express irrespective of the fact that it occurs in homozygous or heterozygous condition. It however, do not suppress another co-dominant allele.

An incomplete dominance allele expresses partially. If in homozygous condition, the expression is full.

The following table summarises the conditions for expression for various types of dominance.
Allele of Dominance Type Homozygous Condition Heterozygous condition Example
Dominant Allele Expresses Expresses Hairy character
Recessive Allele Expresses Do No Express Example: Haemophilia
Incomplete Dominance Allele Fully Expresses Partially Expresses example is Mirabilis Jalapa
(4 o'clock flower)
Co-dominant Allele Expresses Expresses Roan character in cattle

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