Ch.27: Population Genetics Flashcards
Describe polymorphism
the observation that many traits display variation within a population and can describe a gene that commonly exists as 2 or more alleles in a population; occurs when two or more alleles influence a phenotype
What are the two fundamental calculations for population genetics?
-The allele frequency formula allows us to calculate the frequency of alleles in a population
-The genotype frequency formula allows us to calculate the frequency of genotypes in a population
What is the allele and genotype frequencies for a given trait?
always less than or equal to 1
What is the allele and genotype frequencies for polymorphic genes?
frequencies of all of the alleles should add up to 1.0
What does the Punnett Square analysis give?
the same result mathematically
as the Hardy Weinberg equation p2 + 2pq + q2 = 1
What are 4 mechanism that alter existing genetic variation?
-Natural Selection
-Random genetic drift
-Migration
-Nonrandom mating
What is Darwinian (relative) fitness?
a quantitative assessment of the relative likelihood that a genotype
will survive and contribute to the gene pool of the next generation; the values (w) is a measure of reproductive superiority
and it should not be confused with physical fitness
What are the 4 ways that
natural selection may operate?
-Directional selection
-Balancing
-Disruptive or diversifying selection
-Stabilizing selection
Describe directional selection
favors individuals at one extreme of a phenotypic distribution
that are more likely to survive and reproduce in a particular environment
What does directional selection affect?
the Hardy-Weinberg equilibrium and allele frequencies by favoring the extreme phenotype as determined by w, the relative fitness value
What does the mean fitness of the population, (wU), formula allows us to calculate?
changes in the allele frequencies, genotype frequencies
What are the 2 types of balanced polymorhpisms?
-Heterozygote advantage: the heterozygote has a higher fitness than either homozygote
-Negative frequency-dependent selection: the fitness level of a genotype decreases when its frequency becomes higher- rare individuals have a higher fitness level than the more common individuals and are more likely to reproduce
What is the selection coefficient used for?
to determine the allele
frequencies of populations with polymorphisms when the
polymorphisms reach equilibrium
What do disruptive/diversifying selection favor?
the survival of two or more different genotypes with different phenotypes
What happens in a stabilizing selection?
the extreme phenotypes are selected against
Describe genetic drift
-refers to random changes in allele frequencies due to random fluctuations
-In a large population, N = 1000, it takes longer for genetic drift to occur than in a small population, N = 20
-In small populations, N = 20, an allele can become fixed
or be lost very quickly
What can genetic drift be impacted by? What happens if fixation occurs?
-either the bottleneck effect or the founder effect
-how many generations is it likely to take depends on the number of
individuals in the population
What is the bottleneck effect?
In nature, a population can be reduced dramatically in size by a natural disaster that eliminates
individuals regardless of their genotype
What is the founder effect?
A small group of individuals separates from a larger
population and establishes itself in a new location
What is the coefficient of inbreeding is also called?
fixation coefficient, F;
Health studies have shown that a F of less than 5% is desire
New mutations may be..?
-Beneficial
-Neutral
-Deleterious
-Neutral and deleterious mutations are far likelier to occur than beneficial mutation
What are important notes about repetitive sequences?
-they differ from person to person and can be used diagnostically in DNA fingerprinting
-matches between the child and the mother and father should be different
-the % matches between the mother or father and the child should be around 50%
What can you do with DNA from a crime scene?
amplify, probe, and run on a gel to identify a suspect
