adaptation 5 - population differentiation Flashcards
importance of neutral markers
impact of neutral processes on evolution!!!
selection isn’t acting on neutral markers
Does knowing impacts of drift in one population predict impacts in diff pop of same species?
NOPE!!! experience drift independenty
Does knowing impacts of drift on one polymorphic locus allow you to predict what you’ll observe at another polymorphic locus in same pop??
NOT SPECIFICALLY!!!! however, all polymorphic loci within a pop have the same pop size, and pop size is important in determining how drift acts!!
large ROH meaning
runs of homozygosity
large indicates inbreeding and small population size
long term effects of drift on isolated populations
gen. diversity lost over time in isolated, especially in small pops
can carry away currently favoured variation, and favoured in future, and expose deleterious recessive alleles
gene flow def
the mvmt of individuals or propagules from one pop to another, resulting in incorporation of gen. material from one place into another (migration)
Migration together with interbreeding!!!!!!
expected patterns of gene flow
all else equal:
more migration occurs btwn nearby populations
more migration occurs out of large populations
*** ASYMMETRY OF GENE FLOW
key differences btwn mutation and migration gene flow
migrants carry ALL alleles
values of migration are orders of magnitude larger than values for mutation rates
Fst
measure of differentiation btwn pairs of populations
Subpopulation
a part of the total population of a species
Total (T)
total of all individuals pooled tgth across all populations
Equation for Fst
Fst = (Ht - HbarS) / Ht
HT = expected heterozygosity based on assuming whole set of individuals is one pop at HW equilibrium
HS = expected heterozygosity in each subpop with it’s unique allele frequencies
Fst = 0 btwn pops
pops have identical allele frequencies
HT = Hs = 0 therefore Fst = 0
Fst = 1
different alleles are fixed btwn two populations
Hs = 0
Ht - 0 / Ht = 1
Range of Fst
0 to 1 BUT most times in between!!!
Use of Fst
most often, when considering populations within a species, show gene flow
Fst tends to be…
lower btwn pops of same species
higher in species that disperse little
hard to compare among unrelated groups of species
What does 0.09 - 0.11 Fst for sitka spruce show
approx 90% total genetic variation shared across all populations in the range
relationship between genetic distance and geographic distance
greater geo associated with greater genetic
isolation by distance
greater geo dist. associated with greater genetic dist.
reps outcome of two forces:
- gene flow (move/mix alleles)
- genetic drift (produces random divergence btwn pops)
when wouldnt we expect isolation by distance?
gene flow very high
signature of recent founding of populations, freq losses of populations, signatures of chance long-distance dispersal
could be related to environmental difference rather than distance
relation btwn climate and distance
climate and distance COULD have same impact on genetic differentiation
Qst
reps differentiation in quantitative trait values
interpreted the same as Fst
GWAS
genome wide association study
see if differences in traits between pops map onto the genome
regions of genome that influence a quantitative trait = quantitative trait loci (QTL)
show likelihood of of region of the genome influencing a quantitative trait????
Good things abt gene flow
When high levels of homozygosity in a population/small population - intro genetic variance thus ability to adapt and up resistance to disease etc.
New alleles that could be beneficial
Reduce the effects of drift (esp in small pops) that would lead to loss of alleles, inbreeding, upped homozygosity
Allows alleles that arose by mutation in one population to spread to another, trait spread across range of species by gene flow then increase in frequency in populations where it is beneficial
pops connected by gene flow better at responding to changing conditions, bc contain more potentially relevant variation
BAD things abt gene flow
if diff alleles fav at diff locations, counteracts selection therefore lowering mean fitness of population
pops well suited to local environments negatively impacted by gene flow from pops with diff conditions
Reintro. not selected for alleles to population
If high Fst btwn populations, therefore high genetic similarity/homozygosity, chance events more likely to lead to extinction because of low variance
Does gene flow help or hinder local adaptation?
