Genetic Mutations (Bio 303 Quiz #3)

Mutation

An alteration in DNA sequence

Point mutation (or base substitution)

A change in one base pair to another

Insertion/Deletion

The addition or removal of nucleotides

Frameshift mutation

A mutation caused by insertions or deletions

Missense mutation

A nucleotide change that codes for a different amino acid

Nonsense mutation

A triplet changed to a stop codon

Silent mutation

A codon is altered but encodes the same amino acid

Loss-of-function (LOF)

A mutation that reduces or eliminates the function of the gene product

Null (complete LOF)

A complete loss-of-function

Gain-of-function (GOF)

A mutation resulting in enhanced, new, or negative gene functions

most are dominant

Dominant negative (GOF)

A type of gain-of-function mutation where the gene product interferes with the wild-type product

Constitutively active (GOF)

A type of gain-of-function mutation where the gene product is always on

Haploinsufficiency

A type of dominant loss-of-function mutation

Regulatory mutation

A mutation that affects the regulation of gene expression, typically in gene control regions or transcription factors

Somatic mutation

A mutation that occurs in any cell excluding germ cells

it is not heritable

Germ cell mutation

A mutation that occurs in sperm or eggs

it is heritable and can be expressed in all cells of the progeny

Autosomal mutation

A mutation that occurs on any chromosome except for the sex chromosomes

X-linked or Y-linked mutation

A mutation that occurs on the sex chromosomes

Spontaneous mutation

Mutations that occur randomly, are not associated with specific agents, and are accidental

Induced mutation

Mutations that are influenced by external factors (like UV radiation or chemicals) and induce a specific change

Mutagen

An agent that causes mutations

Tandem repeat

A short segment of nucleotides repeated several times, back-to-back, often considered mutation "hot spots"

Tautomeric forms

Alternate chemical forms of nucleotides that allow pairing with noncomplementary bases, potentially leading to permanent base-pair changes

Depurination

The loss of one base in the double helix, usually a purine

Deamination

The process where an amino group in Cytosine (C) or Adenine (A) is converted to a keto group

Base analogs

Mutagens that can substitute for a nitrogenous base (e.g., 5-Bromouracil)

Alkylating agents

Mutagens that donate an alkyl group to nucleotides (e.g., EMS)

Intercalating agents

Mutagens whose size and shape allows them to wedge between base-pairs (e.g., Ethidium Bromide)

Adduct-forming agents

Mutagens that covalently bind DNA (e.g., Acetylaldehyde)

Pyrimidine dimers

Structures created by UV radiation, occurring most often with adjacent thymines

Transposable elements (transposons, jumping genes)

Elements that move around the genome, potentially disrupting gene function

Proofreading

A function of DNA polymerase that catches 99% of replication errors by detecting mispairs and using its 3’ to 5’ exonuclease activity to remove the incorrect nucleotide

Mismatch repair (MMR)

A repair system that deals with errors remaining after proofreading

it detects mismatches, cuts the new DNA strand, removes the damaged region, and replaces it with correct nucleotides

Base excision repair (BER)

A repair pathway used to fix specific kinds of damaged bases, where a specific glycosylase recognizes and removes the damaged base (e.g., uracil)

Nucleotide excision repair (NER)

A repair pathway that corrects “bulky” lesions that distort the double helix, such as pyrimidine dimers caused by UV radiation

Homologous recombination repair (HRR)

A double-strand break repair pathway where information from the homologous chromosome or sister chromatid is used to correct the break

Non-homologous end joining (NHEJ)

An error-prone double-strand break repair system where two broken ends are glued (ligated) together

Xeroderma pigmentosum (XP)

A condition resulting from defects in DNA repair proteins (especially those involved in NER), leading to extreme sensitivity to UV radiation, skin abnormalities, and a high rate of cancer

Incomplete (partial) dominance

A situation where neither allele is dominant, and heterozygotes express an intermediate phenotype

Codominance

The joint expression of both alleles, where heterozygotes make both allelic variations of the gene

Multiple alleles

When some genes have more than two possible alleles (e.g., human blood type alleles)

Recessive lethal alleles

Alleles where death of the individual results from having two copies

Dominant lethal alleles

Alleles where one copy of the dominant allele leads to the death of the individual (rare, e.g., Huntington's Disease)

X-linked genes

Genes located on the X chromosome that display phenotypes associated with a particular sex

Pleiotropy

When a single gene has multiple phenotypic effects (e.g., Marfan syndrome)

Polygenic

A trait influenced by many genes

Complementary gene interaction

A type of multiple gene interaction where a wild-type allele for each gene is required for the trait (resulting in a 9:7 in F2 generation)

Epistasis (Epistatic gene interaction)

When the expression of one gene masks or modifies the other gene

Epistatic allele

The allele that performs the masking

Hypostatic gene

The gene that is being masked

Recessive epistasis

A type of epistasis where the epistatic allele is homozygous recessive (resulting in a 9:3:4)

Dominant epistasis

A type of epistasis where only one copy of an allele is epistatic (resulting in a 12:3:1)

Redundant genes

A multiple gene interaction where only one dominant allele for either gene is sufficient to produce the phenotype (resulting in a 15:1)

Penetrance

The percentage of individuals showing some degree of expression of a mutant genotype

Expressivity

The range of expression of mutant genotypes

Position effect (Position effect variegation)

When the expression of a particular gene is influenced by its physical location relative to other genetic material

Heterochromatin

Tightly wound (condensed) DNA that exhibits little or no gene expression

Euchromatin

Loosely wound (de-condensed) DNA that is associated with active gene expression

Temperature-sensitive mutations

Mutations that produce different phenotypes depending on the temperature (e.g., an enzyme only functional at lower temperatures)

Nutritional mutations

Mutations that produce different phenotypes depending on available nutrients (e.g., Phenylketonuria, PKU)

Genetic anticipation

A phenomenon where genetic expression shows a progressively earlier age of onset and increased severity with each successive generation.