Lecture 6 Flashcards
Change in genotype does not mean
change in phenotype
phenotypic plasticity
the capacity of an organism of a given genotype to express different phenotypes under different environmental condtions
phenotypic plasticity
the capacity of an organism of a given genotype to express different phenotypes under different environmental conditions
phenotypic plasticity example
tadpole can speed up rate of metamorphism if the habitat is drying
norm of reaction
the variety of different phenotypic states that can be produced by a single genotype under different environmental conditions
Norm of reaction example
flys abdominal bristles varry depending on the temperature of there enviorment
genotype x environment interaction simple def
the ability of the environment and genotype to influence each other, example the temp can effect the genotype
genotype x enviorment interaction
the effects of enviormental differences on a phenotype differs among genotypes
at any locus a population may contain one or more
alleles
polymorphism
presence of two or more alleles
wild type
very common allele
allele frequency
the relative commoness or rarity of an allele
sexually reproducing diploid organisms can be
homozygote or heterozygote
homozygote
carry 2 copies of the same allele
heterozygote
carry 2 copies of 2 different alleles
Genotype frequency
the proportion of a population that has a certain genotype
Genotype and —- frequency go hand in hand
allele
If you alter genotype frequency you alter
allele frequency
The proportions of genotypes are related to
allele frequencys
Alteration of genotype frequencies in one generation will
alter the allele frequencies in the gametes and alter the genotype frequencies of the successive generations
Factors that cause frequency to change are
the causes for evolution, frequencies don’t change on there own
hardy-weinberg principle is
the heart of population genetics
hardy weinberg definition
If no evolution is occuring then an equilibrium of allele frequencies will remain in effect in each succeeding generation of sexually reproducing individuals
Allele frequencys remain — under hardy weinberg equlibrium
constant
If we have no evolutionary change then
allele frequencies stay the same
Hard weinberg princible
whatever the inital genotype frequencys for two alleles may be, after one generation the genotype frequencies will be p2, 2pq, q2
p2+2pg+q2=1 is the
genotype frequency
p+q=1 is the
allele frequency
Unless other factors should change them the — and — should stay constant in succeeding generations
allele and genotype frequencys
when genotypes have the frequencies predicted by the hardy weinberg principle they are in
hardy weinberg equilibrium
the hardy weinberg princible is the foundation of
population genetics for sexually reporducing organisms
2 important implications of HW princible
genotype frequencys attain HW values after a single generation of random mating and genotype and allele frequencies remain unchanged across generations (if a new mutation arises it will remain at a very low allele frequency)
Hardy weinberg only holds under
certain assumptions
Hardy weinberg 5 assumption
- Mating is random (panmictic)
- The population size is infinity large
3.Genes are not added from outside the population
4.Genes do not mutate from one allelic state to another
5.All individuals have equal probabilities of survival and reproduction
Population size is infinitly large assumption
eliminates changes in gene frequencies that would occur by change alone like genetic drift
genes are not added from outside the population assumtion
mating among individuals from different populations is called gene flow or migration
genes do not mutate from one allelic state to another assumption
mutation can change allele frequencys
All individuals have equal probability of survival and reproduction assumption
there is no natural selection operating on the population
Why is hardy weinberg useful if the assumptions almost never hold true
allows us to test for evolutionary processes and provides a control for all the major factors that cause evolutionary change within a population
Factors that cause evolutionary change within a population are
nonrandom mating, genetic drift, gene flow, mutation, natural selection
linkage
physical association of genes on the same chromosome
Linkage disequilibrium
the nonrandom association of alleles at different loci, we expect alleles close together to travel together
the hardy weinberg assumptions are
the drivers of evolutionary change
loci are at linkage disequilibrium when
frequency of association of different alleles is higher/lower than what would be expected if the loci were independent and associated randomly
linkage disequilibrium is broken down by
recombination, this will result in linkage equilibrium
Reasons for linkage disequilibrium
nonrandom mating, new mutation arises, recombination being low, population formed by union of 2 populations with different allele frequency, natural selection
Quantitative trait definition
a measurable phenotype that depends on the cumulative actions of many genes and the environment
Quanitive traits
can vary among individuals to produce continuous distribution of phenotypes like hight, weight
Distribution of quanitative variation
normal distribution curve
Polygenic
the genetic component of quantitative variation, doesnt account for enviorment
Additive alleles
combine to produce a heterozygote that is phenotypically the average of the two corresponding homozygotes
Variation that doesnt come from genotype comes from
the enviorment
Vg
genetic variance
Ve
enviormental variance
Vp
how much variation there is, phenotypic variation
Phenotypic variation is
the sum of environment variation and the sum of genetic variation
heratibility
the proportion of the phenotypic variance that is genetic
heritability equasion
h^2=Vg/(Vg+Ve)
We can estimate heritability by
looking at correlations between parents and offspring
Gene flow definition
the exchange of alleles between populations
how gene flow happens
genes can be carried by individuals or games, only migration succeeds in reproducing contributes to gene flow
Gene flow by individuals
person, animals, seeds, spores
gene flow by gametes
pollen, marine animal gametes
Gene flow homogenizes the populations of a species by
bringing them all to the same allele frequencies (unless opposed by natural selection/genetic drift)
Fixation index definition
A measure of the variation in allele frequency among populations
Fixation index range
0-1, 0 means no variation 1 means populations are fixed for different alleles
We use Fst for
measure of genetic similarity among populations within a species to identify the extent of isolation/uniquness
Isolation by distance and gene flow
the further apart two or more populations are from one another geographically the more genetically dissimilar they are
Ring species and gene flow
Two populations which do not interbreed are living in the same region and connected by a geographic ring of populations that can interbreed
