Difference Between X Inactivation and Genomic Imprinting

The key difference between X inactivation and genomic imprinting is that X inactivation is the process by which one copy of X chromosome is inactivated in some females, while genomic imprinting is a process that depends on parent of origin and it is the process in which copies of genes are differentially expressed.

X inactivation and genomic imprinting are two processes that can lead to monoallelic expression. In simple words, both phenomena cause the turning off of one copy of a gene. Genomic imprinting takes place in specific genes, while X inactivation causes inactivation of genes in the entire X chromosome. However, both processes result in decreased gene expression.

CONTENTS

1. Overview and Key Difference
2. What is X Inactivation 
3. What is Genomic Imprinting
4. Similarities Between X Inactivation and Genomic Imprinting
5. Side by Side Comparison – X Inactivation vs Genomic Imprinting in Tabular Form
6. Summary

What is X Inactivation?

X inactivation takes place in some females. It is the inactivation of one X chromosome, which becomes a transcriptionally inactive structure in X inactivation. Once this occurs, this X chromosome will remain inactive throughout the lifetime of the cell and its descendants in the organism. The inactivated X chromosome condenses into a compact structure called a Barr body, and it is stably maintained in a silent state.

X inactivation process depends on the control of two non-coding complementary RNAs. Moreover, X inactivation can occur randomly or due to imprinting. In addition, X inactivation does not happen in males, who have only one X chromosome.

What is Genomic Imprinting?

Offspring inherits two copies of genes from its parents. One copy comes from the mother and the other from the father. Both copies of the gene are often functional or in the active form. In some instances, only one gene copy remains in its active form while the other is in the inactive form. Therefore, one copy is turned “on” while the other is turned “off”. Thus, this is the process called genomic imprinting. Genomic imprinting primarily takes place during the initial stages of development of an organism, and it does not obey the rules of traditional Mendelian inheritance. Moreover, in genomic imprinting, the gene copy that is active depends on the parent of origin.

In humans, only a small percentage of genes undergo genomic imprinting. The majority of genes are not capable of undergoing genomic imprinting. However, this also helps in identifying evolutionary relationship patterns. Furthermore, the imprinted genes usually cluster together in chromosome regions. In humans, there are two major clusters of imprinted genes in the short (p) arm of chromosome 11 and the long (q) arm of chromosome 15.

Genomic imprinting can cause diseases due to deletions or mutations in imprinted genes. Some examples of such kind of genetic diseases are Prader-Willi syndrome, Angelman syndrome, male infertility and some types of cancers.

What are the Similarities Between X Inactivation and Genomic Imprinting?

• One gene copy can be turned off due to both X inactivation and genomic imprinting.
• Both lead to genetic diseases.

What is the Difference Between X Inactivation and Genomic Imprinting?

X inactivation refers to the inactivation of one entire X chromosome in some female mammals. In contrast, genomic imprinting refers to the differential expression of the copies of genes depending on the parent of origin. So, this is the key difference between X inactivation and genomic imprinting.

Moreover, X inactivation occurs in the entire X chromosome, while genomic imprinting occurs in some specific genes. Therefore, we can consider this as another difference between X inactivation and genomic imprinting.

Summary – X Inactivation vs Genomic Imprinting

X inactivation is the process in which one entire X chromosome becomes inactivated in some females. In contrast, genomic imprinting is the process in which two copies of a gene are differentially expressed. It depends on the parent of origin. Genomic imprinting does not obey the traditional Mendelian rules of inheritance. Both X inactivation and genomic imprinting are responsible for the monoallelic expression of genes. However, X inactivation takes place in the entire X chromosome while genomic imprinting takes place in some specific genes. Thus, this is the key difference between X inactivation and genomic imprinting.

Reference:

1. “What Are Genomic Imprinting and Uniparental Disomy? – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, Available here.
2. “X Chromosome: X Inactivation.” Nature News, Nature Publishing Group, Available here.

Image Courtesy:

1. “Human X-Inactivation” By Lilymclaughlin01 (CC BY-SA 4.0) via Commons Wikimedia
2. “Imprt” By Arvid Ågren and Andrew G. Clark – [1][2] (CC BY 2.5) via Commons Wikimedia