IB DP Biology HL D1.3 Mutations and gene editing Flashcards

[q] D1.3.1—What are gene mutations? 

What are substitutions, insertions and deletions?

[a] Gene mutations involve structural changes to genes at the molecular level;

Substitutions: A single nucleotide is replaced by another, potentially changing a single amino acid in a protein.

Insertions: One or more nucleotides are added into the DNA sequence, which can cause a frameshift.

Deletions: One or more nucleotides are removed from the DNA sequence, which can also cause a frameshift.

[q] D1.3.2—What is the consequence of single base substitutions?

[a] Base substitutions result in single-nucleotide polymorphisms (SNPs);

Due to the degeneracy of the genetic code, a base substitution might:

Not change the amino acid (silent mutation);

Change one amino acid in the polypeptide;

Result in a stop codon (nonsense mutation), terminating the polypeptide prematurely.

[q] D1.3.3—Consequences of insertions and deletions

[a] Insertions and deletions can lead to frameshift mutations;

altering all of the 3 bases read, called the reading frame of the gene;

This often results in nonfunctional polypeptides due to major changes in the amino acid sequence;

Premature stop codons;

[q] D1.3.4—Causes of gene mutation

[a] Gene mutations can be caused by:

Mutagens: Chemicals (e.g.,benzene,formaldehyde);

radiation; UV rays; X-rays etc;

Errors in DNA replication or DNA repair;

[q] D1.3.5—Randomness in mutation

[a] Mutations are random and can occur anywhere in the genome;

Some bases are more likely to mutate due to their chemical properties or place in the genome;

No natural mechanism exists to deliberately mutate a specific base to change a trait.

[q] D1.3.6—Consequences of mutation in germ cells and somatic cells

[a] Mutations in germ cells (sperm or egg) can be inherited;

affecting the offspring’s genome;

Mutations in somatic cells affect only the individual, potentially leading to diseases like cancer;

Mutations are random;

[q] D1.3.7—Mutation as a source of genetic variation

[a] Gene mutations are the original source of genetic variation;

Most mutations are harmful or neutral to individuals but essential for species evolution;

Mutations provide the raw material for natural selection, driving evolutionary change;

favourable mutations are naturally selected for and passed on through inheritance;

[q] D1.3.8—Gene knockout as a technique for investigating the function of a gene

[a] Gene knockout involves disabling a gene to study its function;

Libraries of knockout organisms exist for some model species, aiding research;

[q] D1.3.9—Use of the CRISPR sequences and the enzyme Cas9 in gene editing

[a] CRISPR-Cas9 is used for precise gene editing;

Example of successful use: Correction of genetic disorders in research settings;

e.g. Sickle cell anameia;

Ethical issues include potential misuse and long-term effects;

There is an international effort to make regulations consistent for genome editing technologies.

[q] D1.3.10—Hypotheses to account for conserved or highly conserved sequences in genes

[a] Conserved sequences are similar or identical across species or over evolutionary time;

Hypotheses for conservation:

Functional requirements: Essential gene products need the sequence to be the same;

Slower mutation rates: Certain regions mutate less frequently, maintaining their sequences.

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