Mutation and Sheez chapter 4 Flashcards
is a heritable
change in the base sequence of that genome, that is, a change that
is passed from the mother cell to progeny cells. Mutations can lead
to changes in the properties of an organism; some mutations are
beneficial
mutation
a strain of an organism or a virus isolated from nature is called the ( BLANK) and therefore contains the wild-type genome
wild-type strain
A cell or virus derived from the wild type whose genome carries a change in nucleotide sequence is called a
mutant
is a process of isolating mutants based on their ability to survive and grow under specific environmental conditions, conferring a clear advantage to the mutant strain
Selection
involves examining a large number of colonies for specific phenotypic changes without relying on a selective advantage. Mutants may not necessarily have a growth advantage under the conditions tested.
Screening:
is almost always the preferred strategy over screening in genetic experiments. This is because selective conditions impose severe constraints on the population, making mutants easily detectable. In contrast, screening involves looking for mutants without necessarily knowing the specific conditions that favor their growth.
selection
A technique for screening nutritional auxotrophs. It involves transferring colonies from a master plate to a replica plate with agar lacking a specific nutrient. Mutant colonies unable to grow on the nutrient-deficient medium can be identified.
Replica Plating:
is a mutant strain with an additional nutritional requirement compared to the wild type or parental strain from which it was derived.
Auxotroph
is the wild type or parental strain that does not have the additional nutritional requirement and serves as the baseline reference.
Prototroph
Occur without external intervention and result from occasional errors in DNA replication, particularly in base pairing by DNA polymerase.
Spontaneous Mutations
Caused by environmental agents and can include mutations intentionally induced by humans. Inducers can be natural radiation (such as cosmic rays) or various chemicals that chemically modify DNA.
Induced Mutations
Definition: Mutations that change only one base pair in the DNA sequence.
Occurrence: Result from a single base-pair substitution in the DNA.
Phenotypic Impact: Many point mutations may not cause a phenotypic change, although the genotype of the organism is altered.
Dependence on Phenotypic Change: The phenotypic impact of a point mutation depends on the specific location in the genome where the mutation occurs and the nature of the nucleotide change.
Point Mutations:
A point mutation that changes one base pair in the DNA, resulting in a different amino acid in the polypeptide sequence. It can lead to altered protein activity or function.
Missense Mutation
A type of point mutation that does not change the amino acid sequence despite a change in the DNA sequence. Typically occurs in the third base of the codon due to the degeneracy of the genetic code
Silent Mutation
A point mutation that creates a premature stop (nonsense) codon in the DNA, leading to the incomplete synthesis of a polypeptide. Truncated proteins are often inactive or lack normal activity.
Nonsense Mutation
Mutations, where one purine base (A or G) is substituted for another purine, or one pyrimidine base (C or T), is substituted for another pyrimidine.
Transitions
Point mutations in which a purine base is substituted for a pyrimidine base, or vice versa.
Transversions:
Any deletion or insertion of a single base pair in the DNA sequence results in a frameshift mutation.
Frameshift Mutations:
n: Point mutations are typically reversible through a process known as
Reversion
A strain in which the original phenotype, changed by mutation, is restored by a second mutation.
Revertant
- Which class of mutation, missense or nonsense,
is more common, and why?
Missense mutations are generally more common than nonsense mutations. The prevalence of missense mutations is primarily due to the redundancy and degeneracy of the genetic code.
the process by which an organism’s deoxyribonucleic acids (DNA) change, resulting in a gene mutation
Mutagenesis
How do mutagens cause mutations?
Mutagens, both chemical and physical, induce mutations through various mechanisms. Chemical mutagens include base analogues, which mimic DNA bases, alkylating agents causing mispairing, and deaminating agents altering base-pairing. Radiation, such as ionizing and ultraviolet radiation, can directly damage DNA by causing breaks or thymine dimers. Certain chemicals or agents cause insertion or deletion mutations, shifting reading frames. Transposons, mobile genetic elements, can disrupt genes by moving within the genome. Oxidative damage from reactive oxygen species may lead to mutations during repair. Replication errors and error-prone repair mechanisms, like non-homologous end joining, can introduce mutations. Despite cells having repair mechanisms, excessive DNA damage or errors in repair can lead to mutation accumulation, potentially resulting in diseases or altered traits in organisms.
