Study Guide: Mutations [Biology]

Before we get into the topic of mutation, lets define the word. A helpful definition is that "A Mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene." (Blamire, n.d). This means that any change in either phenotype or genotype that was unintentional, can be called a mutation. This post will cover the types of mutations, common places / processes that allow for mutations to happen, as well as some of the common effects that mutations may have on an organism.

---

Types of Mutation

There are a few main types of mutation that can occur, these types are classified based on their effect on the phenotype of an organism.

Deletion

A deletion mutation is when a base is deleted in the copied mRNA strand. When a base(s) is deleted, the grouping for amino acids is all shifted, ultimately altering anything after this error. Eg:

Normal Strand: AAC GCA CUG C

Mutated Strand: AAC GCU GC

Insertion

Similarly, an insertion mutation is when a base is added into the copied mRNA strand. As mentioned with the deletion mutation, by inserting a base, the grouping for amino acids is all shifted ;altering anything after this error. Eg:

Normal Strand: AAC GCA UGC

Mutated Strand: AAC GCA GAU GC

Substitution

A substitution mutation is simply the incorrect copying of a single nucleotide base, resulting in the incorrect letter being coded for in the mRNA strand. Unlike the other two mutation, a substitution mutation only effects the amino acid in the grouping where mutation occurred. * Eg:

Normal Strand: AAC GCA UGC

Mutated Strand: AAC GCU UGC

* As there are multiple codes for some amino acids, a substitution mutation doesn't always result in a different amino acid being coded for.

Frame Shift:

A frameshift mutation is the result of either an insertion or deletion mutation involving only one nucleotide base. By adding or deleting one base, the groping for amino acids is all shifted by one place (either to the left or to the right). Eg:

Normal Strand: AAC GCA UGC A

Mutated Strand: ACG CAU GCA

Silent

A silent can occur as a result of a substitution mutation. As there are multiple base codes for certain amino acids, changing a single base may still allow for the same amino acid chain to be coded for. Eg:

Normal Strand: AAC GCA UGC

Amino acids coded: Asparagine Alanine Valine

Mutated Strand: AAC GCU UGC

Amino Acids Coded: Asparagine Alanine Valine

(Zang, November 12)

---

Can Mutations be Passed On?

A mutation in an organism is classified as either somatic or germline,

A germline mutation refer to mutation that occur in cells that will later develop into sex cells (Ovum in females, and sperm in males). These mutations are then included in mitosis, and are passed down to offspring. (National Cancer Institution, n.d)

A somatic mutation however is a mutation that occurs in any ordinary cell in an organism, and as it is not directly involved in forming a zygote, the mutation cannot be passed on to offspring.

---

Effects of Mutations

Mutation can have no effect on an organism, or can have a major effect on an organism. A commonly looked at example in HSC biology is Down syndrome. For those of who you don't know, Down syndrome is caused when a mutation in the replication process in gametes results in extra genetic information from chromosome 21 (an individual will have three copies of the chromosome instead of just two).

A second disease that also comes up in the HSC course is Sickle Cell anemia. People with this disease have two mutated copies of the gene that is responsible for producing haemoglobin. instead of their cells being disc like shapes (to carry the oxygen around the body) they appear more crescents and half moon shapes; which can often cause blockages and transportation issues.

(Understanding Evolution, n.d)

---

Resources / helpful links:

• https://ib.bioninja.com.au/standard-level/topic-3-genetics/31-genes/mutations.html

• http://www.vce.bioninja.com.au/aos-3-heredity/molecular-genetics/mutations.html

• https://www.yourgenome.org/facts/what-is-a-mutation

Bibliography:

• Blamire J. (n.d). Mutations. Retrieved by: https://www.brooklyn.cuny.edu/bc/ahp/BioInfo/MUT/Mut.Definition.html

• Zang W. (November 2012). Codon and amino acid comparison table. Retrieved by: https://www.researchgate.net/figure/Codon-and-amino-acid-comparison-table_tbl1_261849788

• National Cancer Institution. (n.d). Definition of germline mutation. Retrieved by: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/germline-mutation?redirect=true

• Understanding Evolution (n.d). A Case Study of The Effect of The Mutation: Sickle Cell Anaemia). Retrieved by: https://evolution.berkeley.edu/evolibrary/article/0_0_0/mutations_06

---

So we hope this helped you guys out! The sites we used and added to the resources are all good sources to use and reference if you guys have any assessments or depth studies that need it.

Let us know if this was helpful and what other topics you'd like us to cover!!