Week 10 Flashcards
Population Genetics, Mutation, and Repair
define: phenotypic frequency
the proportion of individuals in a population that are of a particular phenotype
define: genotype frequency
the proportion of individuals in a population that are of a particular genotype
define: allele frequency
the proportion of all copies of a gene in a population that are of a given allele type
what 5 assumptions does the Hardy-Weinberg Law depend on
1) the population includes a very large, number of individuals that all have equal access to mating
2) the individuals mate at random
3) no new mutations appear
4) there is no migration into or out of the population
5) no natural selection
what can you accurately calculate when a population is at Hardy-Weinberg equilibrium
- allele frequency
- genotype frequency
- phenotype frequency
what is the Hardy-Weinberg equation (looking at 2 genes)
p2 + 2pq + q2 = 1
after how many generations do allele frequency for particular gene remain stable at Hardy-Weinberg equilibrium
one
how do you compute genotype frequency
individual possessing the genotype ÷ number of individuals in the sample
how do you compute phenotype frequency
individual possessing the phenotype ÷ number of individuals in the sample
how do you compute allele frequency
(2 x # of homozygous individuals with that allele + # of heterozygous individuals) ÷ (2 x number of individuals in the sample)
how can you check if variation of H-W law expected numbers and expected numbers is significant
perform a chi-square analysis
do allele frequencies change for generation to generation when in H-W equilibrium
no, they do not
define: genetic drift
unpredictable, chance fluctuation in allele frequency that have no effect on survival
what is the relationship between population size and the effects of genetic drift
the smaller the population, the greater the effects of drift
what is the source of most genetic variation in large natural sexually-reproducing populations
recombination due to sexual reproduction, allele shuffling during meiosis
define: genetic natural selection
interactions between genetically determined phenotypes and environmental conditions that cause differential reproduction of certain genotypes
what is an example of natural selection
peppered moth
define: fitness
an individual’s relative ability to survive and transmit its genes to the next generation
what are the two basic components of fitness
viability and reproductive success
define: natural selection (in terms of fitness)
the process that progressively eliminates individuals whose fitness is low and chooses individuals of high fitness to survive and become the parents of the next generation
how is fitness measured
by number of offspring
what holds true about fitness if natural selection does not occur
relative fitness for all genotypes is 1
why is selections unable to reduce the frequency of a recessive lethal allele to zero
when the level of the allele in the population is low, the incidence of homozygotes will be rare; heterozygotes are often unaffected or have advantages
how does time of onset influence the frequency of disease alleles
diseases that cause death after the completion of reproduction will sustain little or no negative selection
define: mutations
heritable changes in base sequences that modify the information content of DNA
what are the two subclasses of base substitution mutations
- transition
- transversion
define: transition mutation
purine for purine, pyrimidine for pyrimidine
define: transversion mutation
purine for pyrimidine, pyrimidine for purine
what are the 5 classes of DNA mutations
1) substitution
2) deletion
3) insertion
4) inversion
5) reciprocal translocation
define: reciprocal translocation
part of one chromosome has been replaced with a region from another chromosome and vice versa
where must mutations occur to be passed on to future offspring
germ cells
how was the Luria-Delbruck experiment conducted
set up small vials of bacterial culture and let them grow for a specified amount of time then add equal portions of each culture to plates containing media along with phage
are mutations caused by selective pressures
no, they occur randomly
what did replica plating verify
spontaneous mutations occur naturally
define: mutagen
any physical or chemical agent that raises the frequency of mutations above the spontaneous rate
what causes mutations
- natural processes of deamination
- UV light
- errors by DNA polymerase
define: depurination
removal of a purine base, allows substitution of another base during replication
what causes deamination
nitrous oxide
what does deamination cause
transition substitutions during replication
how many mutated daughter cells does deamination have
half
what type of mutations does ionizing radiation cause
deletion
what mutation does UV radiation cause
thymine dimers, causing a kink in the DNA strand
what cleaves thymine dimers in bacteria
photolyase
what enzyme repairs base excision
glycosylase
what does Xeroderma Pigmentosum cause
inactive endonuclease, excision repair cannot occur
what type of mutation does oxidation cause
transversion mutation
how often do replication errors occur
once per 109 base pairs
which enzymes keep the rate of replication errors low
proofreading activity of DNA pol I and III
what enzyme helps DNA polymerase with mismatch repair
exonuclease, removes mispaired bases during synthesis
how does mismatch repair after DNA replication occur
relies on tagging parental strands with methyl groups
what are mutations that cannot be corrected
unequal crossing-over and transposon movement
how does red colourblindness occur
deletion in red gene
how does green colourblindness occur
deletion in green gene
how does red and green colourblindness occur
unequal crossing-over
how does blue cone monochromacy occur
deletion of long-range control element -> no transcription of red or green genes
what are examples of somatic cell mutations
- persons with one blue eye and one brown eye
- some types of cancer
- aging
