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D1.3.1—Gene Mutations as Structural Changes to Genes at the Molecular Level:

• Mutation Definition:
  • Alteration in the DNA sequence that can lead to changes in the structure, function, or regulation of genes.
  • Can occur through base substitutions, insertions, or deletions.

Types of Mutations:

• Base Substitution (Point Mutation):
  • Replacement of one nucleotide with another.
  • Can be silent (no change in amino acid), missense (changes amino acid), or nonsense (introduces premature stop codon).
• Insertion:
  • Addition of one or more nucleotides into the DNA sequence.
  • Shifts the reading frame if not in multiples of three.
• Deletion:
  • Removal of one or more nucleotides from the DNA sequence.
  • Shifts the reading frame if not in multiples of three.
• Insertion and Deletion both cause “Frameshift mutations” or the domino effect caused by the insertion or deletion of a gene

D1.3.2—Consequences of Base Substitutions:

• Single-Nucleotide Polymorphism (SNP) Definition:

  • Variation in a single nucleotide base at a specific position in the genome among individuals.

  • Common type of genetic variation.

  • SNPs may change the encoded amino acids (nonsynonymous) or can be silent (synonymous) or simply occur in the noncoding regions. They may influence promoter activity (gene expression), messenger RNA (mRNA) conformation (stability), and subcellular localization of mRNAs and/or proteins and hence may produce disease.

• Impact of Base Substitution:
  • Coding Sequences:
    • Silent: No change in the amino acid sequence.
    • Missense: Alteration in one amino acid.
    • Nonsense: Introduction of a premature stop codon.
  • Noncoding Sequences:
    • Affects regulatory elements, splicing sites, or gene expression levels.
• Genetic Code Degeneracy:
  • The redundancy of the genetic code mitigates the effects of mutations.
  • Allows for multiple codons to code for the same amino acid.
• Types of Base Substitution Mutations:
  • Same-Sense: Codon change that does not alter the amino acid sequence.
  • Nonsense: Results in a premature termination codon.
  • Missense: Substitution of one amino acid for another.

D1.3.3—Consequences of Insertions and Deletions:

• Frameshift Mutation Definition:
  • Insertion or deletion of nucleotides that disrupts the reading frame of the genetic code.
  • Shifts the codon reading frame.
• Impact on Polypeptide Structure and Function:
  • Can lead to significant changes in the amino acid sequence.
  • Often results in nonfunctional or truncated proteins.

D1.3.4—Causes of Gene Mutation:

• Causes of Gene Mutation:
  • Spontaneous:
    • Errors during DNA replication, repair, or recombination.
  • Induced:
    • Exposure to mutagens such as radiation, chemicals, or viruses.
• Mutagen Definition:
  • Substances or agents that increase the rate of mutation.
  • Can be natural or synthetic.

D1.3.5—Randomness in Mutation: