Difference Between Gene and Allele – Definition and Examples

What is Gene?

• A gene is a fundamental unit of heredity that plays a crucial role in determining the traits of an organism. It is a segment of DNA (Deoxyribonucleic Acid) that encodes specific biological instructions. Genes are responsible for guiding the development, growth, and reproductive processes of living organisms by providing the necessary instructions for synthesizing proteins.
• The central dogma of molecular biology describes the flow of genetic information from DNA to RNA and then to protein. Genes are transcribed into RNA molecules through a process known as transcription. This RNA is then translated into proteins during translation. Proteins, in turn, carry out various functions within the organism, including influencing immune responses and hormone production, as well as determining physical characteristics such as hair color, height, blood group, and eye color.
• Genes are inherited from an organism’s parents and are pivotal in the transmission of traits from one generation to the next. They determine an organism’s genotype, which in turn influences the phenotype or observable characteristics.
• Within a gene, there are distinct regions known as coding and non-coding regions. The coding regions, or exons, are transcribed into RNA and eventually translated into proteins. Conversely, non-coding regions, known as introns, are not translated into proteins but have essential roles in regulating gene expression and other cellular processes.

What is Allele?

• An allele represents a variant form of a gene that occupies the same location on a chromosome, known as the gene’s locus. Alleles are essential for determining the diversity in phenotypic traits among individuals. For instance, while a gene might control a trait such as eye color, different alleles of that gene can lead to variations like brown or blue eyes.
• Each individual possesses two alleles for every gene, inherited from each parent. These pairs of alleles can be either identical or different. When an individual has two identical alleles for a gene, they are described as having a homozygous genotype. For example, the genotype TT denotes homozygosity for tall stature. Conversely, when the alleles differ, the individual is termed heterozygous, as in Tt, where T represents tallness and t represents shortness.
• The concept of dominance and recessiveness further characterizes alleles. Dominant alleles overshadow the effects of recessive alleles. Thus, an individual with two dominant alleles (BB) or one dominant and one recessive allele (Bb) will exhibit the dominant trait. Conversely, a recessive trait only manifests when both alleles are recessive (bb).
• A practical illustration of alleles is seen in the ABO blood type system. The alleles IA and IB determine the A and B blood types, respectively, while the allele i denotes type O blood. This example highlights how different alleles can result in distinct phenotypic expressions even within the same gene.

Differences Between Gene and Allele

Understanding the concepts of genes and alleles is crucial in genetics. While both terms are fundamental to the study of heredity, they refer to different aspects of genetic information. Here, we explore the distinctions between genes and alleles, outlining their roles and characteristics in a systematic manner.

The following points highlight their differences in detail:

1. Definition and Function:
   • Gene: A gene is a segment of DNA that encodes instructions for synthesizing proteins, which ultimately affect an organism’s traits. It functions as a unit of heredity.
   • Allele: An allele is a variant form of a gene. Each gene can have multiple alleles, which result in different versions of the same trait.
2. Trait Determination:
   • Gene: A gene determines a specific trait, such as blood type or flower color.
   • Allele: Alleles are responsible for the variations of the trait determined by the gene. For example, different alleles of a gene for flower color might result in red, white, or pink flowers.
3. Expression of Traits:
   • Gene: While a gene dictates the potential traits, it does not express the specific variations on its own.
   • Allele: Alleles are directly involved in the expression of specific variations of a trait, such as the shade of hair color.
4. Number and Pairing:
   • Gene: A gene is located at a specific locus on a chromosome and generally exists as a single entity.
   • Allele: Alleles exist in pairs, with one allele inherited from each parent. These pairs can be identical (homozygous) or different (heterozygous).
5. Occurrence in Organisms:
   • Gene: Genes are present in all living organisms and are essential for the genetic blueprint of any species.
   • Allele: Alleles are particularly relevant in diploid organisms where they contribute to genetic diversity within a species.
6. Pairing:
   • Gene: Genes do not occur in pairs; each gene is a discrete segment of DNA.
   • Allele: Alleles always occur in pairs for each gene, reflecting contributions from both parents.
7. Genotype and Phenotype:
   • Gene: The genotype refers to the genetic constitution of an organism, including all of its genes.
   • Allele: Alleles influence the phenotype, which is the observable expression of traits such as eye color or blood type.
8. Role in Population Diversity:
   • Gene: Genes provide the basic genetic information necessary for the development of traits.
   • Allele: Alleles introduce variation within a population, creating genetic diversity. This variation can influence evolutionary processes.
9. Types and Variants:
   • Gene: A gene is a specific sequence of DNA without inherent categories but can have multiple alleles.
   • Allele: Alleles can be classified into different types, such as dominant versus recessive, or different specific variants of a gene.
10. Genetic Variation:
    • Gene: A gene may have many different alleles, each contributing to different forms of the trait.
    • Allele: The combination of alleles in an individual determines the specific phenotype, which may be dominant or recessive.
11. Examples:
    • Gene: Genes such as those for eye color or blood type are examples where the gene itself represents the trait.
    • Allele: Specific alleles for a gene may result in different eye colors like blue or brown, or different blood types like A, B, AB, or O.
12. Impact on Genetic Disorders:
    • Gene: Certain genes are associated with genetic disorders, such as the gene responsible for cystic fibrosis.
    • Allele: Alleles of a gene can influence the presence or severity of genetic disorders. For example, having two recessive alleles for a specific gene might result in the manifestation of the disorder.
13. Recessive and Dominant Traits:
    • Gene: A gene itself does not display dominance or recessiveness.
    • Allele: Alleles can exhibit dominance or recessiveness. Dominant alleles will mask the expression of recessive alleles in a heterozygous state.
14. Genetic Research and Applications:
    • Gene: Research on genes focuses on understanding their roles and functions within the genome.
    • Allele: Research on alleles often involves studying genetic variation and its effects on traits and diseases.