Difference Between Compound Heterozygote and Double Heterozygote

The key difference between compound heterozygote and double heterozygote is that compound heterozygote is an individual who has two different mutated alleles at a particular gene locus while double heterozygote is an individual who is heterozygous at two separate genetic loci.

Generally, a gene has two alleles since organisms are diploid. Alleles are the variant forms of a gene. They are located in a genetic locus of a chromosome. There are dominant alleles as well as recessive alleles. If an individual has two dissimilar alleles (one dominant and one recessive (Aa)) for a locus, we call it heterozygote. The condition of having two different alleles for a gene is called heterozygous state. Compound heterozygote and double heterozygote are two types of heterozygous situations. Compound heterozygote has two different mutated alleles at a particular gene locus. Double heterozygote is heterozygous at two gene loci.

CONTENTS

1. Overview and Key Difference
2. What is Compound Heterozygote 
3. What is Double Heterozygote
4. Similarities Between Compound Heterozygote and Double Heterozygote
5. Side by Side Comparison – Compound Heterozygote vs Double Heterozygote in Tabular Form
6. Summary

What is Compound Heterozygote?

Compound heterozygote, also called genetic compound, refers to an individual who has two different mutations at a particular gene. Compound heterozygote has two or more heterogeneous recessive alleles at a particular locus, which can cause genetic diseases in a heterozygous state. Both the alleles are mutated. Generally, two copies come from the parent (one from mother and one from father). In compound heterozygous, both these copies harbour mutations that are different. This is a rare situation. It is deleterious and causes the autosomal recessive trait.

Compound heterozygote has been found in nearly all autosomal recessive disorders. When the multiple mutations take place, they affect the gene and the gene product. Ultimately, it can lead to a disease which is a more severe clinical phenotype. Phenylketonuria, Tay–Sachs disease and sickle cell syndrome are several genetic diseases caused by compound heterozygosity.

What is Double Heterozygote?

Double heterozygote is an individual who is heterozygous at two separate genetic loci. In other words, double heterozygote has two different alleles for two genes. It can be shown as AaBb. Heterozygous (Aa) for one gene (locus). At the same time, that individual is heterozygous (Bb) for the other gene (locus). Another double heterozygote can be shown as RrYy. A cross between two double heterozygotes gives 9:3:3:1 phenotypic ratio when the genes are unlinked.

What are the Similarities Between Compound Heterozygote and Double Heterozygote?

• Both compound and double heterozygotes have dissimilar alleles for genes that are considered.
• Mutations of both conditions lead to genetic defects.

What is the Difference Between Compound Heterozygote and Double Heterozygote?

Compound heterozygote is an individual who has two or more heterogeneous recessive alleles at a particular locus which can cause a genetic disease. On the other hand, double heterozygote is an individual who is heterozygous for both genes. So, this is the key difference between compound heterozygote and double heterozygote. In a compound heterozygote, since both alleles are mutated, both the alleles are defective. In contrast, in double hetrozygotes, alleles are not defective, but mutation can lead to disease.

Moreover, compound heterozygote has two recessive alleles for the same gene. And, both alleles are mutated. But, double hetrozygote has two genes for dominant conditions. Thus, this is another difference between compound heterozygote and double heterozygote.

Summary – Compound Heterozygote vs Double Heterozygote

Compound heterozygote has two different mutated alleles at a particular gene locus. Often two alleles are defective in compound heterozygote. Hence, it leads to more severe clinical phenotype. In contrast, double heterozygote is an individual who is heterozygous at two gene loci. Double heterozygote has two genes for dominant conditions. Thus, this is the summary of the difference between compound heterozygote and double heterozygote.

Reference:

1.”Compound Heterozygosity”. En.Wikipedia.Org, 2020, Available here.

Image Courtesy:

1. “Autorecessive” By en:User:Cburnett – Own work in Inkscape (CC BY-SA 3.0) via Commons Wikimedia