HSC Biology: Types of DNA Mutations – Chromosomal Mutations

6 Mins Read | Written by Simon Tang

Key Points Summary

Mutations are a change in the nucleotide sequence of DNA.
Mutations are broken into two different types: base and chromosomal mutations.
Chromosomal mutations are changes to parts or entire chromosomes in a genome.
Examples include aneuploidy, polyploidy, translocation, inversion, deletion, insertion and duplication.

Content

Introduction: What are mutations?

A mutation is a change in the nucleotide sequence of DNA. DNA is the genetic material that codes for who we are, and depending on when mutations occur during our development, these changes in our DNA could lead to physical changes to our body.

What are the different types of mutations?

Mutations are best divided into two sections: Base and chromosomal mutations. This blog goes through chromosomal mutations, but if you want to read about base mutations, click here.

Base mutations occur when bases in a DNA sequence are added, deleted or exchanged for a different base. Remembering that DNA is just a long string of nucleotides (A, T, C, G), base mutations could be like changing a C to a G.
Chromosomal mutations are when sections of whole chromosomes are affected. This is on a much larger scale than base mutations, as thousands, or potentially millions, of bases are affected.

Types of Chromosomal Mutations

Chromosomal Mutations – Distribution

These refer to mutations that affect whole chromosomes.

Aneuploidy typically occurs when a pair of chromosomes fails to separate correctly during meiosis. As a result, we end up with gametes that have two copies of a chromosome, and gametes that have none. If these gametes end up participating in fertilisation, the fertilised egg will have an incorrect number of copies of that particular chromosome. This usually results in monosomy (only one copy of a chromosome) or trisomy (three copies of a chromosome). The normal number is two copies.

Polyploidy occurs when there are additional whole sets of chromosomes. In humans, normal somatic cells are diploid (2n=46 chromosomes). Polyploidy mutations in human cells could result in triploid (3n=39 chromosomes) or tetraploid (4n=92 chromosomes) cells. Polyploidy in humans is fatal, but it is quite common in plants and even viable in some animal species.

Chromosomal Mutations – Rearrangements

These refer to mutations that affect parts of a single chromosome.

Conclusions

So there you have it! Chromosomal substitutions in a nutshell. Click here if you want to learn about base mutations, the other types of mutations you need to know. If you enjoyed this blog and want to know more about how we teach biology at Dymocks Tutoring, give us a ring at (02) 8774 2610 or book a free trial with us!

Chromosomal Mutations	Picture
Translocation: occurs when part of one chromosome breaks off and attaches to the end of a different chromosome. If no part of the chromosome is lost, then this is unlikely to have any effect on the somatic cell. However, if translocation occurs in the gametes, then the translocated portion of the chromosome will either be inherited in two copies, or not inherited at all, potentially causing problems in the offspring.
Inversion: occurs when part of one chromosome breaks off then reattaches in the opposite direction. This may impact the organism if the break point was in the middle of a gene – that gene would then be rendered non-functional.
Deletion: When part of a chromosome is deleted, this usually has a substantial impact on an organism, since entire genes can be lost. Chromosomal deletions can often be fatal.
Insertion: Sometimes, one part of a chromosome may break off and insert itself into a different chromosome. Insertion is often classified as a subset of translocation and results in similar effects.
Duplication: occurs when part of a chromosome is replicated, resulting in several copies of the genes contained. This usually increases the expression of those genes, which can have varying effects on the organism.