Summary Biology Notes: Gene and Chromosomal Mutations

GENE AND CHROMOSOMAL MUTATIONS

Mutations
Permanent alteration of the nucleotide sequence of DNA
● Germline mutation
○ Mutation occurs in germline cells (germ cells and gametes)
○ May be hereditary (transmitted to offspring and successive generations)
○ Genetic disorder: mutation has adverse effect on phenotype of organism
● Somatic mutation
○ Mutation occurs in somatic cells
○ Not inherited by progeny

Gene/point mutations
Involves a change in a single nucleotide pair of a gene
1. Nucleotide substitution
Replacement of one nucleotide pair with another
● Effects:
A) Missense mutation
● Nucleotide substitution in DNA sequence changes the mRNA codon ->
translation of a different amino acid
● Amino acid sequence of polypeptide changed -> change in specific 3D
conformation of protein -> protein function altered
B) Nonsense mutation
● Nucleotide substitution in DNA sequence changes a codon for an amino acid
into a stop codon -> premature termination of translation -> shorter/truncated
polypeptide
● Change in 3D conformation of protein -> protein function altered (mostly
non-functional)
C) Silent mutation
● Nucleotide substitution in DNA sequence changes the mRNA codon; however,
the same amino acid is inserted into polypeptide due to the degeneracy of
the genetic code
● Amino acid sequence of polypeptide unchanged -> no change in specific 3D
conformation of protein -> protein function not altered
D) Neutral mutation
● Nucleotide substitution in DNA sequence changes the mRNA codon; however,
the resulting amino acid produces no detectable change in the function of the
protein translated -> due to substitution of amino acid with one of similar
physical and chemical properties, or substitution of amino acid residue that
is non-essential to protein’s structure and function
● Amino acid sequence of polypeptide changed -> no change in overall 3D
conformation of protein -> protein function not altered



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