Understanding DNA Mutations and Their Impacts

Mutation

a change in the nucleotide sequence of an organism's DNA

Heritable change

A heritable change in the genetic material

Types of mutations

Rank the following mutations in terms of greatest to least impact on the structure and function of genes and gene products: missense (change amino acids), nonsense (change to 'stop'), frameshift (change reading frame), and silent (no change in the product).

Source of genetic variation

Mutation is the ultimate source of genetic variation.

Random impact of mutation

Mutation is random with respect to its impact on an individual's fitness.

Causes of mutations

Result from the addition or subtraction of a base or the substitution of one base for another.

Role of mutations

Essential to the continuity of life: source of variation for natural selection.

Likelihood of mutations

New mutations are more likely to be harmful than beneficial.

Causes of DNA mutations

Can occur as a result of mistakes during DNA replication or can be caused by environmental mutagens.

Types of errors

Errors can occur in DNA synthesis; DNA can be damaged.

Spontaneous vs Induced mutations

They can be spontaneous or induced.

Spontaneous Mutations

Mutations that arise from abnormalities in biological processes.

Induced Mutations

Mutations caused by environmental agents.

Mutagen

A chemical or physical agent that interacts with DNA and can cause a mutation.

Somatic cells

All other cells that are not reproductive.

Germline cells

Reproductive cells (sperm/egg) that can pass mutations onto the next generation.

Point Mutation

A change in a single nucleotide pair of a gene.

Silent Mutation

A nucleotide pair substitution that has no observable effect on the phenotype.

Missense Mutation

A nucleotide-pair substitution that results in a codon that codes for a different amino acid.

Nonsense Mutation

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

Frameshift Mutation

A mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or deleted is not a multiple of three.

Nucleotide-pair substitution

A type of point mutation in which one nucleotide in a DNA strand and its partner in the complementary strand are replaced by another pair of nucleotides.

Insertion

A mutation involving the addition of one or more nucleotide pairs to a gene.

Deletion

A mutational loss of one or more nucleotide pairs from a gene.

Tautomeric Shift

A change in the structure of nucleotides that can lead to incorrect pairing.

Background mutation rate

Approximately 1 mutation per 1 million genes.

Genetic Variation

Mutations in germline cells are the ultimate source of genetic variation.

Cancer

Mutations in somatic cells can lead to cancer.

Protein Function

Point mutations can affect protein structure and function.

Phenotypic Difference

Silent mutations result in genetic diversity that is not expressed as a phenotypic difference.

Protein Efficiency

Missense mutations may cause proteins to function at a lower efficiency or, on rare occasions, improve efficiency.

Complete Loss of Protein Function

Frameshift mutations usually result in a complete loss of protein function.

Nondisjunction

An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other.

Translocation

An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome.

Mutagens

Agents that alter DNA, which can be natural or artificial.

Disruption of base-pairing

A process where some mutagens modify nucleotide structure, leading to incorrect pairing.

Nitrous acid

A mutagen that deaminates bases so they pair with the wrong nucleotide.

Mustard gas

A mutagen that alkylates bases, adding methyl or ethyl groups.

Disruption of replication

A process where some mutagens insert between the bases and distort the helix.

Benzopyrene

A mutagen found in cigarettes and charbroiled food that disrupts DNA replication.

Genetic disorder

A mutant condition that has an adverse effect on the phenotype.

Thymine Dimer

Two adjacent thymine bases in one DNA strand that cause a buckle and bulge in the strand.

Nucleotide excision repair

A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.

Endonuclease

An enzyme that cuts the damaged DNA strand at two points during DNA repair.

DNA polymerase

An enzyme that fills in the missing nucleotides during DNA repair synthesis.

DNA ligase

An enzyme that seals the free end of the new DNA to the old DNA, completing the strand.

Teams of enzymes

Groups of enzymes that detect and repair damaged DNA, such as thymine dimers.

Ultraviolet radiation

A cause of thymine dimers that distorts the DNA molecule.

Repair synthesis

The process by which DNA polymerase fills in missing nucleotides using the undamaged strand as a template.

Nuclease enzyme

An enzyme that removes the damaged section of DNA during repair.

Mutant condition

A condition resulting from a mutation that adversely affects the phenotype.

Hereditary disease

A genetic disorder that is passed down through generations.