Gene and Allele

Both genes and alleles are essential for the survival of living organisms. Gene is a segment of DNA that codes for a specific protein or enzyme. Allele is one of two or more alternative forms of a gene, located at the same place (locus) on homologous chromosomes.

Gene is carried by an individual in all their body cells, while allele will be found only in specific types of cells such as muscle cells. In other words, these two biological entities are complementary to each other and they differ only in some aspects. Yet, what is the difference between gene and allele? In order to find out the answer for this question, let us explore in this article about how both gene and allele work together with their differences at hand.

What is Gene?

DNA is the primary material which carries the genetic code. It contains millions of nucleotides that are arranged in a linear form. Genes are the segments on DNA which act as instructions to produce a protein or enzyme by reading off a series of three base pairs or ‘letters’ called nucleotides, adenine (A), thymine (T), cytosine (C), guanine (G) and uracil (U).

Alleles are kinds of genes that exist at one DNA loci. They can be homozygous or heterozygous. The alleles are located at the same place (locus) on homologous chromosomes. However, it should be noted that only one allele is carried by an individual in all their body cells. Because of this, both genes and alleles are complementary to each other and they differ only in some aspects.

Gene mutations are responsible for many diseases such as Huntington’s disease, Huntington’s chorea and mitochondrial diseases such as Kearns-Sayre syndrome, MELAS syndrome and Leigh syndrome. Genetic disorders may also cause serious illness such as sickle-cell anemia, cystic fibrosis and Tay-Sachs disease.

Functions of Gene

• Gene codes for protein or enzymes
• Gene can be altered due to mutations
• Gene helps in the production of functional proteins and enzymes

What is Allele?

DNA is the primary material which carries the genetic code. It contains millions of nucleotides that are arranged in a linear form. Alleles are the alternative forms of genes which exist at one DNA loci. They can be homozygous or heterozygous.

Alleles are created from two alleles at the same locus on homologous chromosomes by mutation, recombination or crossing over process. The alleles will be located at the same place (locus) on homologous chromosomes but they differ only in some aspects related to their expressions and activities.

Alleles are responsible for the differences in inherited characteristics between individuals (phenotypes). This is because each individual inherits a pair of genes from their parents. The alleles from both parents interact with each other and produce different gene products, as well as different observable characteristics.

Types of Alleles

There are two types of alleles, dominant and recessive alleles.

Dominant Allele

The DNA segments in the chromosomes which contain a group of genes that determine the phenotype or physical appearance of an individual are known as dominant alleles. A person who inherits a pair of dominant alleles will show the trait or phenotype for that specific gene.

Allele frequency represents the distribution of alleles in a population. Allelic variation at the same gene locus is determined by six factors.

These factors are referred to as the six major components of genetic variation known as QTL (quantitative trait locus) regions.

Recessive Allele

Recessive alleles are alleles which are recessive to a dominant allele at a given gene locus. A person who inherits two recessive alleles for the same gene will not show the expressed phenotype for that particular gene, but individuals may be carriers of one or more recessive alleles. These alleles will be expressed in late generations of an individual in which both recessive and dominant alleles present in the individual’s genes interact with each other (recombination) to produce different phenotypes.

Functions of Allele

• Alleles can be expressed in late generations
• Alleles may be responsible for recessive diseases
• Carriers of one or more recessive alleles may have a very low risk of disease, but carriers of one dominant allele have a higher risk of disease

What is the difference between Gene and Allele?

The main function performed by both genes and alleles is the same, which is coded for protein or enzyme production by reading off DNA on chromosomes (genes). Some key differences between Gene and Allele are:

1) Allele is carried by an individual in all their body cells and genes are carried only by certain cells.

2) Alleles are located at the same place (locus) on homologous chromosomes.

3) An individual may have different alleles of one gene in their genomes.

4) Same gene locus may have allelic variation at the same time, depending on its location to other genes.

5) Genes cannot be “switched off” and there is no mechanism to induce them to express themselves. Alleles can control the expression of genes linked to them, which gives rise to “dynamic variation”.

6) A gene can carry out more than one function and can produce more than one product.

7) An allele cannot carry out more than one function and cannot produce more than one product.

8) Individuals are not born with just a single functional copy of a gene (gene dosage).

9) Dominant alleles will always be expressed in an individual’s phenotypes, while recessive alleles may not be expressed.

10) Dominant alleles will always be expressed in the phenotype of an organism, while recessive alleles need to be present twice to be expressed.

11) Allelic frequencies change over time due to genetic drift and natural selection.

Conclusion

Alleles and genes are the two important terms used to describe the action of a single gene. The two terms are interrelated with each other and each of them has some differences from the other. A person having identical genes for an allelic pair may have different phenotypes due to their presence in different tissues, or different environmental factors or lifestyles, which might change the phenotypic expression. Therefore, it is very important to understand the difference between alleles and genes in order to get a clear idea about inheritance patterns and protein expression.