The key difference between allelic and non allelic gene is that in allelic genes, the alleles are present at the same location of the homologous chromosome while in non-allelic gene, the alleles are present at different locations of the same homologous chromosome to express a particular character.
Mendelian ratios do not explain all types of inheritance patterns. These variations cause different ratios in dihybrids and monohybrids. Allelic and non allelic gene and their interactions explain the deviation of Mendelian traits. These deviations are referred to as interaction of genes or factor hypothesis.
CONTENTS
1. Overview and Key Difference
2. What is an Allelic Gene
3. What is a Non allelic Gene
4. Similarities – Allelic and Non allelic Gene
5. Allelic vs Non allelic Gene in Tabular Form
6. Summary – Allelic vs Non allelic Gene
What is an Allelic Gene?
Allelic gene is an alternative form of a gene that possesses an identical relative position on homologous chromosomes to express a particular character. These genes are responsible for different characteristics. Allelomorph is another term for allelic genes. There are different types of allelic genes based on their interactions. They are incomplete dominance (monohybrid and dihybrid), co-dominance, overdominance, lethal factor, and multiple alleles. During incomplete dominance, the dominant allele does not suppress the other allele completely. It results in an intermediate phenotype, and the heterozygote will be phenotypically distinguishable from homozygotes. During co-dominance, both alleles of the gene are expressed in heterozygotes with phenotypes of both parents.
Figure 01: Allelic Gene
When allelic genes interact and form lethal factor genes, it causes the death of the individual. Death occurs when the allelic genes are dominant. Multiple alleles are another form of allelic gene interactions where two or more alleles are present at the same gene locus of the homologous chromosome to express a particular character.
What is a Non-Allelic Gene?
A non-allelic gene is an alternative form of a gene present at different positions of a homologous chromosome to express a particular character. With their interactions, non-allelic genes could affect one gene over the other during gene expression. These interactions include epistasis (recessive and dominant), inhibitory factor, inhibitory factor with partial dominance, polymorphic gene, duplicate gene, a duplicate gene with dominance modification, and multiple factors (two loci and three loci), simple interaction, and complementary factor. In simple interactions, two allelic gene pairs affect a particular phenotype.
Figure 02: Non-Allelic Genes Undergoing Recombination
Epistasis occurs when a gene or a pair of genes mask the expression of other non-allelic genes. This could be either recessive epistasis or dominant epistasis. In inhibitory factor, the gene shows no phenotype but prevents the gene expression of another non-allelic gene.
What are the Similarities Between Allelic and Non Allelic Gene?
- In both allelic and non-allelic genes, alleles are present in the same homologous chromosome.
- Both affect gene expression.
- They show different interactions.
- These allelic and non-allelic gene interactions are deviations of Mendelian ratios.
What is the Difference Between Allelic and Non Allelic Gene?
The key difference between allelic and non allelic genes is the location of the alleles. In allelic genes, the alleles are present at the same location of the homologous chromosome, but in non-allelic genes, the alleles are present at different locations of the same homologous chromosomes in order to express a particular character. Both genes affect gene expression in different ways due to their interactions.
The below infographic presents the differences between allelic and non allelic genes in tabular form for side by side comparison.
Summary – Allelic vs Non Allelic Gene
Mendalian ratios do not explain all types of inheritance patterns. These variations cause different ratios in dihybrids and monohybrids. Allelic and non allelic genes and their interactions explain these deviations. The key difference between allelic and non allelic genes is the location of the alleles that affect gene expression. But in both genes, these alleles are present on the same homologous chromosome. Allelic and non-allelic genes show different interactions. Some interactions could be lethal and cause death.
Reference:
1. “Gene interactions: Allelic and Non-Allelic.” Biology Discussion.
Image Courtesy:
1. “Gene Loci and Alleles” By Keith Chan – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Non-allelic Homologous Recombination” By Svenskbygderna (talk) – File:Non allelic homologous recombination.png (CC BY-SA 4.0) via Commons Wikimedia
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