The key difference between allele and locus is that the allele refers to one of the two or more alternative sequences of a gene at a certain locus while the locus refers to a certain location on a chromosome where a gene can be found.
In the form of genes, genetic information inherits from parents to offspring. Genes are the specific nucleotide sequences located in the chromosomes. Many genes can be found in the genome of an organism. Their arrangement in the genome is precise, and the location of the gene can be easily found using a genetic marker. Furthermore, a particular gene can have different versions which we name as alleles. The specific location of a gene in the chromosome is also very important, and we call it a locus.
CONTENTS
1. Overview and Key Difference
2. What is an Allele
3. What is a Locus
4. Similarities Between Allele and Locus
5. Side by Side Comparison – Allele vs Locus in Tabular Form
6. Summary
What is an Allele?
An allele is an alternative form of a gene. In simple words, alleles refer to different versions of a gene. There are often two alleles of one gene. But it can vary. More than two alleles may be present in genes. However, they located at the same location as the homologous chromosomes which calls locus. The DNA sequence or the nucleotide sequence differs between alleles of the same gene due to mutations. This leads to different observable phenotypic traits as well as genetic disorders.
Figure 01: Alleles
Humans often have two alleles at each genetic locus since they are diploid and acquire one homologous chromosome from each parent during fertilization. According to the Mendelian genetics, alleles can be either dominant allele or recessive allele depending on their associated traits. A dominant allele can express its phenotypic trait even when the one allele is present. But to express the recessive phenotypic trait, both alleles should be recessive (homozygous recessive) at the locus.
What is a Locus?
A locus (in plural loci) is a location on the chromosome where a gene resides. Most people refer to it as a chromosome marker. A genetic map is a loci ordered list for a certain genome. Gene mapping is the most commonly used process to determine the locus in a certain biological trait.
Figure 02: Loci
When an organism is heterozygous for a particular locus, there are one dominant allele and one recessive allele on it. If the organism is homozygous, he carries either two dominant alleles or two recessive alleles at one locus.
What are the Similarities Between Allele and Locus?
- You can find both allele and locus on chromosomes.
- They are terms associated with genes.
- Alleles locate at the same locus of a gene.
- In genetics, they are really important for many studies.
What is the Difference Between Allele and Locus?
There are thousands of genes present in the chromosomes. Allele and locus are two terms related to chromosomes and the genes. Allele is one of the possible forms of a gene. Usually, there are two types of alleles, dominant allele or recessive allele. On the other hand, the locus is a position on a chromosome where a gene is found. It is a specific location. This is the key difference between allele and locus. Moreover, the locus works as a genetic marker as well. Also, loci are important in gene mapping and constructing a genetic map of an organism. Based on their functions, the difference between allele and locus is that the allele codes for a trait while the locus gives residence to a gene.
The below infographic presents the difference between allele and locus in tabular form.
Summary – Allele vs Locus
Allele and locus differ with each other even though alleles locate at loci. Therefore, the allele is one possible form of a gene. On the other hand, the locus is a specific location on a chromosome where a gene situates. Loci are genetic markers. There can be more than a single allele in one locus. Furthermore, allele codes for a gene, while locus is just a position on the chromosome. This is the difference between allele and locus.
Reference:
1.“Allele.” Wikipedia, Wikimedia Foundation, 24 Aug. 2018. Available here
2.“Allele.” ScienceDaily, ScienceDaily. Available here
Image Courtesy:
1.”Gene Loci and Alleles”By Keith Chan – Own work, (CC BY-SA 4.0) via Commons Wikimedia
2.”Neurofibromatosis2-locus”By Original author unknown, vectorized by Jkwchui (Public Domain) via Commons Wikimedia