Mutations (College Board AP® Biology): Flashcards
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Define mutation.
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Define mutation.
Mutation is a change in the DNA sequence that can alter the type or amount of protein produced, and so change the phenotype of a cell or organism.
How are mutations classified according to their effect on the phenotype?
As:
beneficial — produce useful new traits
detrimental — disrupt gene function, causing disease or loss of function
neutral — have no effect on the phenotype
Define point mutation.
Point mutation is a change to a single nucleotide in DNA, usually a one-base substitution.
Substitution mutation
A mutation in which one nucleotide is switched for another.
Define substitution mutation.
Substitution mutation is a mutation in which one nucleotide is switched for another.
Define frameshift mutation.
Frameshift mutation is a mutation caused by the insertion or deletion of nucleotides, which shifts the reading frame and alters every codon downstream of the mutation.
Define nonsense mutation.
Nonsense mutation is a point mutation that creates a premature stop codon, producing a shortened, non-functional protein.
Define missense mutation.
Missense mutation is a mutation in which an amino acid is changed, altering the resulting protein.
Because the genetic code is , a substitution mutation can be silent and cause no change to the amino acid sequence.
Because the genetic code is degenerate, a substitution mutation can be silent and cause no change to the amino acid sequence.
The insertion or deletion of a nucleotide shifts the frame, altering every codon downstream.
The insertion or deletion of a nucleotide shifts the reading frame, altering every codon downstream.
True or False?
A single-base substitution causes a frameshift mutation.
False.
Frameshift mutations are caused by the insertion or deletion of nucleotides. A substitution changes only one nucleotide and does not shift the reading frame.
True or False?
Frameshift mutations are more likely than substitutions to cause major changes to the amino acid sequence.
True.
A frameshift alters every codon downstream of the mutation, so it usually has a much larger effect than a single-base substitution.
Define mutation.
Mutation is a random change in the DNA sequence that occurs spontaneously during DNA replication or repair.
How can mutations arise during DNA replication?
DNA replication is highly accurate, but errors occur when DNA polymerase incorporates incorrect nucleotides into the DNA sequence.
Which external factors can increase mutation rates?
External factors such as UV radiation and reactive chemicals can increase mutation rates.
How can a mutation alter an organism's phenotype?
A mutation can change the type or amount of protein produced, which in turn alters the phenotype.
True or False?
Whether a mutation is beneficial, detrimental, or neutral depends on the environmental context.
True.
A phenotype that is detrimental in one environment may be beneficial in another, so the effect of a mutation depends on the environmental context.
How does the sickle cell mutation illustrate that a mutation's effect depends on environment?
The sickle cell mutation provides resistance to malaria, making it beneficial in malaria-prone regions even though it can be detrimental elsewhere.
Mutations are a source of , which is essential for the evolution and adaptation of organisms.
Mutations are a source of genetic variation, which is essential for the evolution and adaptation of organisms.
Why are mutations important for natural selection?
A mutation may introduce new alleles into a population, providing the variation on which natural selection or genetic drift can act.
True or False?
Errors in mitosis or meiosis can result in changes in phenotype.
True.
Errors in mitosis or meiosis can alter chromosome number or structure, which can change the phenotype.
Define nondisjunction.
Nondisjunction is the failure of chromosomes to separate correctly during mitosis or meiosis, leading to an abnormal chromosome number.
Define aneuploidy.
Aneuploidy is a condition in which a cell has the wrong chromosome number because one or more individual chromosomes are extra or missing.
Define polyploidy.
Polyploidy is a condition in which a cell has one or more extra sets of chromosomes; for example, a normally diploid (2n) cell may instead be triploid (3n) or tetraploid (4n).
How can changes to chromosome structure affect phenotype?
Structural changes such as inversions, translocations, duplications, or deletions can alter gene expression, changing the phenotype.
of chromosomes during cell division can produce cells with an abnormal number of chromosomes.
Nondisjunction of chromosomes during cell division can produce cells with an abnormal number of chromosomes.
How can mutations lead to evolution by natural selection?
Mutations may create new alleles that affect an individual's phenotype; these changes are then subject to natural selection.
Why is an advantageous allele more likely to increase in frequency in a population?
An advantageous allele allows individuals to outcompete others in the population, so the affected individual is more likely to pass on the beneficial allele to future offspring.
Define sickle cell anemia.
Sickle cell anemia is a disorder caused by a mutation in the hemoglobin gene, which leads to the production of abnormal hemoglobin.
Why is being heterozygous for the sickle cell allele advantageous in some regions of the world?
Heterozygous individuals carry the sickle cell trait without showing symptoms, but are resistant to malaria, giving a survival advantage in areas where malaria is prevalent.
The sickle cell allele is selected for in regions of the world where is prevalent.
The sickle cell allele is selected for in regions of the world where malaria is prevalent.
True or False?
Individuals who are homozygous for the sickle cell allele (Hbs) show symptoms of the disorder.
True.
Homozygous individuals show symptoms, whereas heterozygous individuals carry the trait without symptoms and gain resistance to malaria.
Besides mutation, how can organisms generate new genetic variants?
By recombining alleles in new ways, for example through:
the horizontal acquisition of genetic material in prokaryotes
the recombination of genetic information from viruses
Define horizontal acquisition of genetic material.
Horizontal acquisition of genetic material is the transfer of DNA (often as plasmids) between prokaryotes of the same generation, rather than from parent cell to daughter cell, which increases genetic variation.
Define transformation.
Transformation is a form of horizontal gene transfer in which DNA in the environment is taken up by a cell and incorporated into its own DNA.
Define transduction.
Transduction is a form of horizontal gene transfer in which DNA is transferred from one bacterial cell to another via viral particles (bacteriophages).
Define conjugation.
Conjugation is a form of horizontal gene transfer in which a thin tube, or pilus, forms between two bacteria to allow the exchange of DNA.
Define transposition.
Transposition is the movement of a segment of DNA or genes within a chromosome, or between different DNA molecules such as plasmids and chromosomal DNA.
How does viral recombination increase genetic variation?
When two viruses infect the same host cell, their genetic material interacts during replication, so the virus progeny acquire genes from both strains.
True or False?
Reproductive processes that increase genetic variation are evolutionarily conserved across many organisms.
True.
Because they provide significant benefits to populations, these mechanisms have been evolutionarily conserved over millions of years.
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