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Genetics - Genetic Mutations

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A mutation is defined as a permanent change in the base sequence of DNADNA. These changes can occur spontaneously during DNADNA replication or be induced by external factors.

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Point mutations (Substitutions) occur when a single nucleotide is swapped for another (e.g., AA is replaced by GG). This may result in a silent mutation (no change in amino acid), a missense mutation (different amino acid), or a nonsense mutation (premature stop codon).

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Frameshift mutations occur due to the insertion or deletion of nucleotides. Since mRNAmRNA is read in triplets called codons, adding or removing a base shifts the entire 'reading frame,' usually resulting in a completely different protein structure.

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Mutagens are physical or chemical agents that increase the frequency of mutations. Examples include UVUV radiation, XX-rays, and chemicals like those found in tobacco smoke.

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Genetic mutations are the primary source of genetic variation within a population, which is a driving force for natural selection and evolution.

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Sickle Cell Anemia is a classic example of a point mutation where a single base change in the gene for hemoglobin (substitution of AA for TT) results in the amino acid Valine instead of Glutamic Acid.

📐Formulae

Number of Codons=Total Number of Nucleotides3\text{Number of Codons} = \frac{\text{Total Number of Nucleotides}}{3}

DNA Base Pairing Rule: [A]=[T] and [G]=[C]\text{DNA Base Pairing Rule: } [A] = [T] \text{ and } [G] = [C]

Mutation Rate=Number of MutationsTotal Number of Cell Divisions\text{Mutation Rate} = \frac{\text{Number of Mutations}}{\text{Total Number of Cell Divisions}}

💡Examples

Problem 1:

A segment of DNADNA has the sequence 5′−TAC−GGC−AAT−3′5'-TAC-GGC-AAT-3'. If a mutation occurs and the first GG is deleted, what is the new sequence and what type of mutation is this?

Solution:

The new sequence is 5′−TAC−GCA−AT...−3′5'-TAC-GCA-AT...-3'. This is a deletion mutation leading to a frameshift.

Explanation:

By removing the GG at the 4th position, the remaining bases shift to the left. The original codons were (TAC),(GGC),(AAT)(TAC), (GGC), (AAT). After deletion, the codons become (TAC),(GCA),(AT...)(TAC), (GCA), (AT...), which changes every amino acid coded after the site of mutation.

Problem 2:

In a substitution mutation, the DNADNA codon GAAGAA (which codes for Glutamic Acid) is changed to GAGGAG. Given that GAGGAG also codes for Glutamic Acid, identify the specific type of point mutation.

Solution:

This is a Silent Mutation.

Explanation:

Because the mutation in the third nucleotide of the codon (A→GA \rightarrow G) does not change the resulting amino acid (Glutamic Acid), the protein's primary structure remains unaffected.

Problem 3:

If a protein is composed of 150150 amino acids, calculate the minimum number of nucleotides in the coding region of the mRNAmRNA (excluding the stop codon).

Solution:

150×3=450150 \times 3 = 450 nucleotides.

Explanation:

Each amino acid is coded by a triplet of nucleotides (a codon). Therefore, to find the total nucleotides, we multiply the number of amino acids by 33.

Genetic Mutations - Revision Notes & Key Formulas | IB Grade 9 Science