Chapter 9.3: DNA Mutations Alter DNA Sequence

Flashcards from Chapter 9.3 of Principles of Life, 3rd Edition.

Incorporation error rate

The probability that an incorrect base will be inserted into a new strand of DNA, creating a mismatch

• These are mitigated by proofreading (immediate removal and replacement) and mismatch repair (scanning by a complex for removal and replacement by cellular processes)

Proofreading

A function of DNA polymerases where mismatched nucleotides are removed immediately after being placed down

Mismatch repair

A function of a specialized complex where newly replicated molecules are scanned for helix irregularities, removing and replacing incorrect fragments when found

Point mutation

A mutation that substitutes, deletes, or inserts a single base pair in a DNA molecule

Base-pair substitution

A type of point mutation that leads to a change of a single base pair (A-T to G-C), created through:

• Erroneous replacing of the original instead of the new strand

• Lack of repair before the next round of DNA replication

Tautomers

The two structural isomeric forms of a base; having a rarer form present can result in the incorrect pairing of another base

Deamination

The removal of an amino group in a base, resulting in a different base form; this can result in mispairing that is passed down after replication

Spontaneous mutations

Mutations caused by polymerase errors or spontaneous chemical change in bases

Mutagens

Substances that chemically alter DNA and lead to induced mutations (unlike spontaneous mutations)

• Commonly related to cigarette smoking, certain dietary components, and radiation; these can often be mitigated

Excision repair

The repair of damaged nucleotides with their replacement by normal ones

• Involves proteins that remove the fragment for repair by DNA polymerase and ligase

Silent mutations

Mutations that do not change the amino acid sequence or function of the protein

Loss-of-function mutations

Mutations that occur due to low expression or nonfunctional protein production

• Often recessively inherited, as a wild-type allele usually results in sufficient functional protein

Gain-of-function mutations

Mutations that lead to proteins with altered function

• Often dominantly inherited, as the mutant allele results in a still functioning protein

Conditional mutations

Mutations that affect the phenotype only under certain environmental conditions

• Often seen with temperature-sensitive traits, such as coat color in rabbits

Nonhomologous end joining

The joining of two broken ends without regard for homology, potentially joining separate pieces of DNA to cause chromosomal mutations

Deletion

The loss of a chromosome segment, typically with severe consequences due to gene absences

Duplication

The repetition of a chromosome segment, resulting in multiple copies of that segment

• Occur due to crossing-over errors between homologous chromosomes, producing a deletion in the other chromosome

• Typically have mild effects on phenotype due to over-expression of genes

Inversions

Mutations where a chromosome segment is reversed in sequence

• Occur due to cutting out and rotation, resulting in a reversed sequence in the chromosome

Translocations

Mutations where non-homologous chromosomes exchange segments

• Can potentially be harmless if break points do not interrupt genes, but otherwise can cause erroneous expression