Mutations and Genetic Variation

Flashcards about mutations, mutagens, and genetic variation

What is a mutagen?

A physical, chemical, or naturally occurring agent that causes a change in the DNA sequence.

What are mutations?

Alterations in the DNA of chromosomes, including gene rearrangements like deletions, translocations, duplications, and inversions.

Name some electromagnetic and radiation sources that act as physical mutagens.

UV, X-rays, and Gamma rays.

How does UV light act as a mutagen?

Causes covalent bonds to form between neighboring thymine (T) and/or cytosine (C) bases on the same DNA strand, forming a pyrimidine dimer that can cause DNA polymerase to misread the bases during replication.

How do X-rays and gamma rays act as mutagens?

Waves enter a cell, hit DNA, and their high level of energy is absorbed, knocking electrons out of atoms and breaking chemical bonds within DNA, forming ions.

What are chemical mutagens?

Compounds that cause mutations by altering the chemical structure of DNA bases.

What are base modifiers?

Change the chemical structure of a base, causing DNA polymerase to incorporate an incorrect base during mitosis/meiosis. Examples include alcohol, nitrates in processed meats, and nitric oxide.

What is a base analogue?

Molecule resembling a base that is incorporated into DNA. During the next cell division, DNA polymerase incorrectly matches a base to the analogue. Example: 5-bromouracil.

What is an intercalating agent?

Molecule that inserts between adjacent bases on the same DNA strand, causing DNA to bend or kink. DNA polymerase then deletes or adds an extra base during mitosis/meiosis. Examples include chemicals in cigarettes and acridine.

What are transposons (jumping genes)?

DNA sequences able to move (copy and paste or cut and paste) and insert themselves at a new location in the genome.

How do retroviruses (RNA viruses) act as naturally occurring mutagens?

They directly cause mutations in host cells when they insert their DNA. These viruses convert RNA genome into DNA through reverse transcription, which inserts into host's genome, changing the DNA sequence and potentially inactivating genes.

What are mycotoxins?

Chemicals produced by some fungi that, when ingested, enter cells, are metabolized, and then bind to DNA, causing point mutations. Example: Aflatoxin B1 causes guanine to mutate to thymine.

What are reactive oxygen species?

Naturally occurring chemicals produced during cellular respiration. These molecules contain oxygen, are highly unstable (e.g., superoxide and hydroxyl), and can react easily with other molecules, including DNA. They can break chemical bonds between bases and cause point mutations.

What are point mutations?

Changes in a single nucleotide; includes transitions and transversions.

What is a silent mutation?

Single nucleotide substitution that does not change the encoded amino acid, resulting in no change in the polypeptide sequence. Has no functional effects and is evolutionarily neutral.

What is a missense mutation?

Single nucleotide substitution that results in a change in a single amino acid. The resulting polypeptide may have reduced/increased activity, not form correct tertiary/quaternary structure, or have new functions.

What is a nonsense mutation?

Changes an amino acid to a stop codon. Translation is terminated prematurely, producing a shortened polypeptide that does not function or is degraded by the cell.

What is a neutral mutation?

Changes in DNA that result in an amino acid of the same type, not significantly affecting protein structure. (e.g. positively charged to positively charged)

What is a frameshift mutation?

Insertion/deletion of nucleotides where the number of nucleotides is not divisible by 3, resulting in a frameshift mutation. This causes a complete change in the translated polypeptide sequence from the site of mutation onwards.

What is a chromosomal mutation?

Mutation that affects the structure or inheritance of a chromosome.

What is translocation?

When one or more chromosomes break, and chromosomal fragments rejoin with a different chromosome or to a new site on the same chromosome. This can disrupt gene expression by splitting genes, separating regulatory elements, or fusing genes together.

What is inversion?

Region of chromosome that breaks at two ends, rotates 180 degrees, and reinserts in the reverse orientation on the same chromosome.

What is aneuploidy?

Gain/loss of a chromosome caused by chromosome non-disjunction, where sister chromatids fail to move to opposite poles of daughter cells during cell division.

What are somatic mutations?

Mutations in diploid somatic cells that only affect the individual in which they occur and are not passed on to the next generation.

What is somatic mosaicism?

Condition where a mutation occurs during mitosis causing two populations of cells with distinct genotypes.

What are germ-line mutations?

Mutations occurring in a gamete that can be passed on to the next generation, resulting in the mutation being present in every cell of the offspring's body.

What part of DNA has the most significant impact on an organism's phenotype?

Exons, because they directly affect protein structure.

What are introns?

Located inside genes of eukaryotic organisms, transcribed into pre-mRNA but then spliced out when mRNA is formed prior to translation. Mutations have no impact unless at splice sites.

What are intergenic regions?

Long regions of DNA between genes that contain regulatory elements such as enhancers. Mutations in enhancers affect the binding of transcription factors.

What are telomeres?

Located on tips of chromosomes in eukaryotic organisms. They act as protective 'caps,' preventing deletion of genes on chromosomes.

What are centromeres?

Specialized regions of repetitive non-coding DNA that separate the short and long arms of a chromosome.

How do mutations cause genetic variation?

Point and chromosomal mutations in germ-line cells create new alleles that may be passed on to offspring.

How does meiosis cause genetic variation?

Genetic recombination (crossing over) and random independent segregation/assortment of chromosomes.

How does fertilization cause genetic variation?

Mixing of haploid sets from two parents which creates new allele combinations.

What is the gene pool?

The total amount of genetic variation in a population, measured by allele and genotype frequencies.

What does the Hardy-Weinberg equilibrium principle state?

Allele and genotype frequencies in a population remain constant if mutation, gene flow, genetic drift, and natural selection are not influencing the gene pool.

What is gene flow?

Movement of genes into and out of a population when organisms migrate between areas.

What is genetic drift?

Random fluctuation in allele frequencies in a population, resulting from chance events that influence survival and reproduction of an organism.

What is the bottleneck effect?

A disaster significantly reduces population size of a species, where the small population of survivors may have fewer alleles and different allele frequencies.

What is the founder effect?

Small group of individuals separates from a large population to establish a new colony, where the small size of the new population can lead to strong genetic drift.