Difference Between Gene Mutation and Chromosomal Mutation

Main Difference – Gene Mutation vs Chromosomal Mutation

Gene mutations and chromosome mutations are two types of mutations that occur in the genome of an organism. A mutation is a permanent alteration of the nucleotide sequence of a gene. Gene mutations and chromosomal mutations mainly differ in the magnitude of the alteration. The main difference between gene mutation and chromosomal mutation is that gene mutation is an alteration of the nucleotide sequence of a gene whereas chromosomal mutation is an alteration of the structure or number of chromosomes. Mutations are caused by errors in DNA replication, homologous chromosome segregation or mutagens such as UV and chemicals. They alter the production of functional proteins. The influence of chromosomal mutations is higher than that of gene mutations since the magnitude of mutation in chromosomal mutations is high.

Key Areas Covered

1. What is Gene Mutation
     – Definition, Features, Types
2. What is Chromosomal Mutation
     – Definition, Features, Types
3. What are the Similarities Between Gene Mutation and Chromosomal Mutation
     – Outline of Common Features
4. What is the Difference Between Gene Mutation and Chromosomal Mutation
     – Comparison of Key Differences

Key Terms: Aneuploidy, Chromosome Number Changes, Chromosomal Mutation, Chromosome Structure Alterations, Deletions, Duplication, Gene Mutation, Insertions, Inversion, Missense Mutation, Nonsense Mutation, Point Mutations, Silent Mutation, Translocations

What is a Gene Mutation

A gene mutation is an alteration of the nucleotide sequence of a gene. Gene mutations can be caused by errors in DNA replication during cell division by both mitosis and meiosis. In addition, gene mutations are caused by environmental factors such as UV and chemicals. These factors are called mutagens. Sickle cell anemia, hemophilia, cystic fibrosis, Huntington syndrome, Tay-Sachs disease, and many cancers are caused by gene mutations. The two types of gene mutations are point mutations and base pair insertions or deletions.

Point Mutations

Point mutations are caused by single nucleotide substitutions. Three types of single nucleotide substitutions can be identified as silent mutations, missense mutations, and nonsense mutations. Some single nucleotide alterations can be tolerable since they still produce the same protein due to the degeneracy of the genetic code. This type of a mutation is called silent mutations. Some alterations in the nucleotides may alter the corresponding amino acid. The producing protein comprises different properties compared to the original protein. These types of mutations are called missense mutations. Some alterations of nucleotides may introduce translation inhibiting signals such as stop codons. This type of mutations is called nonsense mutations. Nonsense mutations produce shortened proteins, which are non-functional.

Main Difference - Gene Mutation vs Chromosomal Mutation

Figure 1: Gene Mutations – Point Mutations

Base Pair Insertions or Deletions

Base pairs can either inserted or deleted from the original sequence. This type of mutations is capable of altering the open reading frame. Therefore, they are called frameshift mutations. The process of translation can also be affected by introducing stop codons to the sequence either too early or too late. Gene mutations are shown in figure 1.

What is a Chromosomal Mutation

Alterations of chromosomes are called chromosomal mutations. Chromosomal mutations are mainly caused by errors in crossing over during meiosis. In addition, mutagens may also cause chromosomal mutations. Chromosomal mutations can occur in the structure of the chromosome as well as the chromosome number.

Chromosome Structure Alterations

There are four types of chromosomal structure alterations as translocations, duplications, inversions, and deletions. Translocations are the interchange of segments of chromosomes between non-homologous chromosomes. Duplication is the production of extra copies of genes. Broken chromosomal segments are inverted and again inserted to the same position of the chromosome during inversions. Pericentric inversions encompass a centromere. Paracentric inversions occur in the short and long arms of the chromosome rather than in the centromere. The permanent breakage of segments of chromosomes is called deletions. Some deletions in chromosomes can be lethal.

Difference Between Gene Mutation and Chromosomal Mutation

Figure 2: Chromosome structure alterations
1 – Deletion, 2 – Duplication, 3 – Inversion

Chromosome Number Changes

Some organisms contain an abnormal number of chromosomes. This is called aneuploidy. Aneuploidy occurs due to failures in the homologous chromosome segregation during the anaphase I of meiosis. Chromosome breakage or nondisjunction errors cause the improper segregation of homologous chromosomes. The resultant sex cells may contain missing or extra chromosomes. Klinefelter syndrome and Turner syndrome are sex chromosomal abnormalities. Down syndrome is an autosomal chromosomal abnormality.

Similarities Between Gene Mutation and Chromosomal Mutation

Both gene mutation and chromosomal mutation cause alterations in the genetic material of an organism.
Both gene mutation and chromosomal mutation cause alterations in gene expression.

Definition

Gene Mutation: An alteration of the nucleotide sequence of a gene is referred to as a gene mutation.

Chromosomal Mutation: Alterations in the chromosome structure or chromosome number are referred to as chromosomal mutations.

Cause

Gene Mutation: Errors in DNA replication and mutagens such as UV and chemicals cause gene mutations.

Chromosomal Mutation: Errors in crossing over during meiosis cause chromosomal mutations.

Change

Gene Mutation: The alteration occurs in the nucleotide sequence of a gene in a gene mutation.

Chromosomal Mutation: The alteration occurs in a segment of a chromosome in chromosomal mutations.

Number of Genes Affected

Gene Mutation: A single gene is affected by a gene mutation.

Chromosomal Mutation: Several genes are affected by a chromosomal mutation.

Influence

Gene Mutation: The influence of gene mutation is comparatively low.

Chromosomal Mutation: Chromosomal mutations can sometimes be lethal.

Disease

Gene Mutation: Sickle cell anemia, hemophilia, cystic fibrosis, Huntington syndrome, Tay-Sachs disease, and cancers are caused by gene mutations.

Chromosomal Mutation: Klinefelter syndrome, Turner syndrome, and Down syndrome are caused by chromosomal mutations.

Conclusion

Gene mutation and chromosomal mutations introduce alterations to the genetic material of a particular organism. Gene mutations are the alterations of the nucleotide sequence of a gene. Gene mutation may alter the function of proteins in the body. Chromosomal mutations can be either an alteration of chromosome structure or chromosome number. The influence of chromosomal mutations is higher than gene mutations. The main difference between gene mutation and chromosomal mutation is the magnitude of alterations that occur in the genetic material by each type of mutation.

Reference:

1.Bailey, Regina. “How Gene Mutation Occurs.” ThoughtCo. N.p., n.d. Web. Available here. 29 July 2017.
2. Bailey, Regina. “How Chromosome Mutations Occur.” ThoughtCo. N.p., n.d. Web. Available here. 29 July 2017.

Image Courtesy:

1. “Point Mutation” By NCI – (Public Domain) via Commons Wikimedia
2. “Single Chromosome Mutations” By Richard Wheeler (Zephyris)Vector version: NikNaks – File:Single Chromosome Mutations.png. (CC BY-SA 3.0) via Commons Wikimedia