Main Difference – Gene vs Allele
Both genes and alleles are responsible for the genetic make-up of a life. Genes are sequences which are found on chromosomes. They encode the instructions for the development, functioning, and reproduction – the different traits of an individual. Each trait consists of two factors called alleles in diploid organisms. The observable factor is called the dominant allele. The hidden factor is called the recessive allele. The key difference between gene and allele is that a gene is a stretch of DNA which determines a specific trait and an allele brings variations to a single trait.
This article explains,
1. What is a Gene
– Structure, Characteristics, Functions
2. What is an Allele
– Structure, Characteristics, Functions
3. What is the difference between Gene and Allele
What is a Gene
A gene is a region (locus) or a sequence on chromosomes. It encodes an amino acid sequence of a specific protein. Thousands of genes can be found within a single chromosome of higher organisms. The gene is recognized as the molecular unit of hereditary. The genetic instructions transfer into progeny via reproduction through genes. Gene sequence is transcribed into RNA; RNA is translated into proteins. This is called as the central dogma of molecular biology.
In prokaryotes, the genes group to form units called operons. Operons contain functionally related genes which are transcribed together. Eukaryotic genes consist of exons, introns and untranslated regions. Prokaryotic genes lack introns. Genes are transcribed with introns. Consequently, they are removed by splicing of exons. Multiple proteins can be produced by alternative splicing. Gene expression is regulated at transcriptional and translational level.
Figure 1: Structure of a Gene
What is an Allele
A variant form of a particular gene is referred to as an allele. It creates a different phenotypic trait. But most gene variations are silent, which means they do not generate an observable difference; however, the sequence is a variant. Diploid organisms carry homologous chromosomes. The same gene can be found in the same loci of each chromosome within the homologous pair. If these two loci contain exactly the same sequence, the two alleles are considered as homozygous at the locus. On the other hand, if the two loci contain sequence differences, two alleles are considered as heterozygous at the locus. When an allele pair is heterozygous, one of the phenotypic traits is normally dominant and the other is recessive. This is called complete dominance where only the dominant allele has expressed.
The dominant allele is common in nature and is called as the wild type. The recessive allele is comparatively rare and is called the mutant. Sometimes, neither allele in the pair is dominant, thereby both alleles are expressed. This condition is identified as co-dominant; human AB blood type inheritance is an example of co-dominant allele expression. Incomplete dominance occurs when one allele in the pair is partially dominant over the other allele. An example for the incomplete dominance is the color inheritance of pink flower in tulips. Dominant and recessive alleles describe the genotypic interactions between the two alleles. This interaction was first described by Gregor Mendel in 1860s. On the contrary, some genes consist of multiple alleles. For example, ABO blood type is determined by IA, IB and IO alleles.
Figure 2: Codominant inheritance of the ABO blood groups.
Difference Between Gene and Allele
Definition
Gene: A gene is a segment of DNA which control a specific trait.
Allele: An allele is a variant of a particular gene. It exhibits different phenotypic variations in the sane trait.
Number Involved
Gene: A single gene determines a particular trait.
Allele: Two or multiple alleles bring variations to the trait.
Location
Gene: Genes are found in all known organisms.
Allele: Alleles can be identified in multi-genome organisms.
Occurrence
Gene: Genes occur as individual units.
Allele: Alleles always occurs in pairs.
Influence
Gene: Genes encode for a single protein.
Allele: Alleles produce opposite phenotypes.
Genetic Make-up
Gene: Genes create the individual.
Allele: Alleles bring differences to individuals in a population.
Examples
Gene: Eye color, Blood group, Skin color.
Allele: Eye color: blue, green or brown eyes, Blood group: A, B, O and AB, Skin color: white skin, black skin.
Conclusion
A gene is considered as the molecular unit of hereditary. That means, genes are the things that we inherit from our parents. Alleles determine the limit of expression of the genes. Therefore, alleles always occur in pairs. Alleles also determine the trait of some genes. Hence, the main difference between gene and allele is in its variations created to the trait.
Reference:
1. Schleif R. Genetics and Molecular Biology. 2nd ed., The Johns Hopkins University Press, 1993, pp. 22-47, Accessed 09 Feb. 2017
2. “Allele”. Wikipedia, the free encyclopedia. 2017. Accessed 13 Feb. 2017
3. Bailey R. “Allele – A Genetics Definition”. About education. 2017 . Accessed 15 Feb. 2017
Image Courtesy:
1. “Gene” By Courtesy: National Human Genome Research Institute – (Public Domain) via Commons Wikimedia
2. “ABO system codominance” By GYassineMrabet This vector image was created with Inkscape. – Own work based on Codominant.jpg (Public Domain) via Commons Wikimedia
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