Exam 4: Microbial Genetics II Mutation Types and Causes Flashcards
What is a mutation? Why do mutations occur? Are mutations good or bad? Explain.
Random haritable charitable change in the nucleotide sequence of DNA. Mistakes, relatively rare, typically occur during DNA replication. Most have insignificant effect to or no effect on phenotype. If they do have an effect far more mutations have deleterious effects than have a beneficial effect upon the individual.
Alterations can be passed to daughter cells in unicellular organisms. In multicellular organisms mutations in reproductive cells can be passed to offspring.
Describe the relationship between mutation, natural selection, and evolution?
Mutations are the ultimate source of genetic variation and natural selection acts upon this genetic variant. Without mutations there’s no genetic variation and thus no evolution.
Under what conditions or during what times are mutations more likely to occur?
Most likely to occur during DNA replication. If a population is small and isolated then inbreeding will increase the incidence of existing mutations.
What effect do most mutations have on the fitness of an organism?
Most are deleterious and are likely to decrease the fitness of an organism.
What effect do most mutations have on the function of a gene?
Most mutations will inhibit the function of the gene. That can be turning it on when it’s not supposed to be or keeping it off when it should be off.
If a mutation does affect gene function, is it more likely to impair function or to improve function? Explain.
Most likely will impair the function causing the function to deviate from its normal status.
Give at least one specific example of a deleterious mutation.
Antennapedia- drosophila (fruit flies) have legs instead of antennae.
Sickle cell, cystic fibrosis, tay sachs disease.
Give at least one specific example of a beneficial mutation.
Lactose tolerance- historically humans were lactose intolerant, they drink milk from their mother then milk consumption ends and the lactose processing gene is turned off. However mutation occurred where individuals continued to possess the lactose gene into adulthood, giving them the ability to drink milk throughout life. With the advancements of farming and access to milk products they had another food source they could use. This was an advantage giving them an edge to stay alive and ultimately reproduce, giving the gene to future generations.
Globally outside the US most people still contain the wild type gene and cannot produce lactose. Lactose production is still the minority on a global scale.
Antibiotic resistance- advantageous to bacteria.
What is mutation rate?
Likelihood a gene will be altered by a new mutation. Expressed as the number of new mutations in a given gene per cell generation.
What factors affect mutation rate?
Type of mutation in question- varies mutation to mutation.
Size of gene- bigger gene more likely for mutations.
Chromosomal location of gene- some areas are more likely to have mutations then others.
Species studied
Strain of species studied
Efficiency of the DNA repair systems
Presence of mutagens- like radiation
What is mutation frequency?
Refers to the prevalence of a particular mutant allele in a population. Frequency of a particular mutation is initially very low because the mutation rate is very low.
What factors affect mutation frequency?
Will vary depending on location for example the rate of blue eye mutation might be the same everywhere but the frequency will change depending on the population you evaluate. Natural selection can significantly alter the frequency of the mutation allele. Deleterious alleles commonly decrease in frequency while beneficial alleles commonly increase in frequency.
All mutations are initially rare. Do they all remain rare? Explain.
Yes, initially all mutations are rare. But there are factors that can increase their frequency. Radiation, antibiotic usage, and mutagens can increase the frequency of mutations.
Antibiotic bacteria resistance rate might be very low but if you look at samples from individuals you might find that these bacteria are resistant to penicillin. The initial rate of the mutation was very low but with more prevalent use of penicillin an environment was created that selected for individuals that were resistant. Frequency went up but the mutation rate stays low.
What is a chromosomal mutation?
Changes in chromosome structure. X-rays are great at causing breaks in chromosomes then errors occur when the body tries to fix it. e.g Deletions, insertions, and translocations.
What is a genome mutation?
Changes in chromosome number. E.g. Trisomy 21 “down syndrome”. In most cases 3 copies of chromosomes produce nonviable embryos so are rarely seen except for with chromosome 21.
What is a single-gene mutation?
Relatively small changes in DNA structure, occur within a single gene.
What is a point mutation?
Point mutations affect a single base pair. Two main classes are substitutions and insertions/deletions.
What is a base substitution mutation?
One nucleotide substituted for another. Two types transitions and transversions.
What is an insertion mutation?
One more nucleotides added.
What is a deletion mutation?
One or more nucleotides removed.
What is a transition mutation?
Type of base substitution. Pyrimidine changed to another pyrimidine, C-> T. Purine changed to another purine, A->G. More likely to occur than transversions as it is easier to mix them up.
What is a transversion mutation? How hard is it to make?
Type of base substitution. Purine and pyrimidines are interchanged, A->C or G and C-> A or G. Harder mistakes to make so are less common than transitions.
