Difference Between Nondisjunction and Translocation Mutations

The key difference between nondisjunction and translocation mutations is that the nondisjunction mutation is a mutation that occurs due to the failure in segregation of homologous chromosomes or chromatids during the cell division while the translocation mutation is a mutation that occurs due to the rearrangement of different parts of chromosomes between non-homologous chromosomes.

Mutation is an alteration of the nucleotide sequence of a DNA molecule in the genome of a particular organism. Thus, mutations occur mainly due to the errors of cell divisions (mitosis and meiosis). Therefore, depending on the type of mutation, its effect varies. Accordingly, nondisjunction mutation and translocation mutation are two major types of mutations that occur during cell division.

CONTENTS

1. Overview and Key Difference
2. What are Nondisjunction Mutations
3. What are Translocation Mutations
4. Similarities Between Nondisjunction and Translocation Mutations
5. Side by Side Comparison – Nondisjunction vs Translocation Mutations in Tabular Form
6. Summary

What are Nondisjunction Mutations?

Nondisjunction refers to the failure in segregation of homologous chromosomes or chromatids during mitosis or meiosis. However, the effect of nondisjunction varies among the mitosis and meiosis. In mitosis, nondisjunction results in various cancers. In meiosis, nondisjunction results in two different daughter cells; one daughter cell has both parental chromosomes with the other daughter cell has none. Consequently, this causes a mutation in the number of chromosomes due to an extra chromosome or missing chromosome.

The chromosomal disorders that occur due to nondisjunction during meiosis are Down’s syndrome, Klinefelter’s syndrome, Turners’ syndrome, etc. Down’s syndrome or Trisomy 21 occurs due to nondisjunction of chromosome 21 during meiosis where the individual inherits three copies of chromosome 21 instead of two. Hence, an individual who has Down’s syndrome has 47 chromosomes instead of the usual 46.

Turners’ syndrome develops due to the nondisjunction of sex chromosomes during meiosis. The affected individual has 45 chromosomes with a single X chromosome. The term that refers to this mutation is monosomy of the X sex chromosome. In such an individual, the sex genotype is XO. Either way nondisjunction in both mitosis and meiosis results in fatal disease conditions.

What are Translocation Mutations?

In the context of genetics, translocation is a chromosomal abnormality resulting due to rearrangement of different parts of the chromosomes between non-homologous chromosomes. Hence, this abnormality often results in defective mutations such as cancer and infertility. It is easy to identify chromosomal translocations through cytogenetics or by a karyotyping of affected cells. Moreover, translocations occur inter-chromosomally or intra-chromosomally.  Interchromosomal translocations occur within a single chromosome while intrachromosomal translocations occur between chromosomes. During the translocation mutation, a part of the chromosome breaks off and joins again at a different location.

Also, there are different categories of translocation mutations; they are the balanced, unbalanced, reciprocal, and non-reciprocal translocation. Firstly, in balanced translocations, equal exchange of materials takes place without extra or missing genetic information. However, unbalanced translocations result in extra or a missing gene due to an unequal exchange of chromosome material.  In reciprocal translocations, exchange of genetic material takes place between non-homologous chromosomes. Finally, in non-reciprocal translocations exchange of genetic material takes place from one chromosome to a non-homologous chromosome.

Translocation mutations cause cancers such as leukaemia, infertility and XX male syndrome, etc. Infertility occurs when one of the parents carries a balanced translocation resulting in non-viable fetus even though the parent conceives. XX male syndrome occurs due to the translocation of the SRY gene of the Y chromosome to X chromosome.

What are the Similarities Between Nondisjunction and Translocation Mutations?

• Nondisjunction and Translocation Mutations are genetic mutations.
• They both can occur during both mitosis and meiosis.
• Furthermore, both types result in cancer and Down’s syndrome.
• Also, both can affect sex chromosomes.

What is the Difference Between Nondisjunction and Translocation Mutations?

Nondisjunction and translocation mutations are alterations of the nucleotide sequences of DNA molecules that can cause various disease conditions. Nondisjunction mutations occur due to the failure of homologous chromosomes or chromatids to segregate correctly during the cell division. On the other hand, translocation mutations occur due to the rearrangement of different parts of chromosomes between the chromosomes after breaking off from one chromosome. Thus, nondisjunction mutations cause abnormalities in the number of chromosomes in a cell while translocation mutations cause structural abnormalities of the chromosomes in the genome of organisms. Hence, this is the key difference between nondisjunction and translocation mutations.

The below infographic on the difference between nondisjunction and translocation mutations a more descriptive comparison.

Summary – Nondisjunction vs Translocation Mutations

Mutations occur due to errors of cell division. Nondisjunction mutation is the failure in segregation of homologous chromosomes or chromatids during mitosis or meiosis. In short, this is the difference between nondisjunction and translocation mutations.

Furthermore, the effect of nondisjunction varies in mitosis and meiosis. In mitosis, nondisjunction results in cancer. The chromosomal disorders that occur due to nondisjunction during meiosis are Down’s syndrome, Klinefelter’s syndrome and Turners syndrome. On the other hand, translocation mutation is a chromosomal abnormality that results due to the rearrangement of different parts between non-homologous chromosomes. Inter-chromosomal, intra-chromosomal, balanced, unbalanced, reciprocal, and non-reciprocal translocations are the types of translocation mutations.

Reference:

1.Study.com, Study.com. Available here 
2.“Aneuploidy & Chromosomal Rearrangements.” Khan Academy, Khan Academy. Available here 

Image Courtesy:

1.”Mitotic nondisjunction”By Wpeissner – Own work, (CC BY-SA 3.0) via Commons Wikimedia 
2.”Translocation-4-20″By Courtesy: National Human Genome Research Institute (Public Domain) via Commons Wikimedia