IB DP Biology D1.3 Mutations and gene editing Study Notes - New Syllabus -2025
IB DP Biology D1.3 Mutations and gene editing Study Notes – New syllabus 2025
IB DP Biology D1.3 Mutations and gene editing Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Biology syllabus with guiding questions of
- How do gene mutations occur?
- What are the consequences of gene mutation?
Standard level and higher level: 3 hours
Additional higher level: 2 hours
D1.3.1—Gene mutations as structural changes to genes at the molecular level
- DNA is a very stable molecule that carries genetic information.
- Base sequences of DNA are copied with high accuracy during cell replication.
- Cells have methods to correct errors in DNA replication.
- Changes in DNA molecules can still occur.
- Gene mutation is a change in the base sequence of a gene.
- Gene mutations are random and should be distinguished from deliberate changes made by molecular biologists when editing genes.
Types of Gene Mutations
- Substitution: One base in the coding sequence of a gene is replaced by a different base.
- Can happen due to chemical changes to bases or errors during DNA replication.
- The most common type of substitution is G to T.
- Insertion: An extra nucleotide is inserted into the sequence of the gene.
- Requires a break in the sugar-phosphate backbone of the DNA molecule.
- Deletion: A nucleotide is removed from the sequence of the gene.
- Requires two breaks in the sugar-phosphate backbone.
Multiple insertions and deletions can occur, affecting two or more consecutive nucleotides.
Important Note: Gene mutations are random and should not be confused with the deliberate changes made by molecular biologists when editing genes.
D1.3.2—Consequences of base substitutions
-Mostly neutral or deleterious: The effects of base substitution mutations are often neutral or harmful. In some cases, they can even be lethal.
– Non-coding DNA: Base substitutions in non-coding DNA between genes are unlikely to have any effect.
– Coding sequences: Only changes to the coding sequences of genes can affect the amino acid sequences of polypeptides.
– Same-sense mutations: These mutations change one codon for an amino acid into another codon for the same amino acid. They do not affect the phenotype, but they may make it possible for a second mutation to change the codon into one for a different amino acid.
– Nonsense mutations: These mutations change a codon that codes for an amino acid into a stop codon. This results in the termination of translation before a polypeptide is completed, and the resulting protein usually does not function properly.
– Mis-sense mutations: These mutations alter one amino acid in the sequence of amino acids in a polypeptide. They may have little effect if the new amino acid has a similar structure and chemical properties to the original one, or if it is positioned in a non-critical part of the protein. However, mis-sense mutations can also have severe and even lethal effects. Many genetic diseases are caused by mis-sense mutations, such as sickle cell disease.
– Beneficial mutations: A very small proportion of mis-sense mutations improve the functioning of a protein and increase an individual’s chances of survival. Although rare, these mutations are arguably more significant because they contribute to evolution and adaptation. When a base substitution mutation occurs in one individual and is inherited by offspring, a new allele of one gene is produced, increasing the genetic diversity of the population.
Single-Nucleotide Polymorphisms (SNPs)
– When the DNA from individual humans is sequenced, large numbers of base substitutions are found that have happened at some time in the past.
– These are known as single-nucleotide polymorphisms, frequently abbreviated to SNPs and pronounced “snips.”
– SNPs can occur in noncoding regions of DNA.
– The presence of some SNPs is associated with certain diseases.
– Correlations between SNPs and diseases allow scientists to look for SNPs to determine an individual’s genetic predisposition to develop a disease.