BIO 201 EXAM 2 WITH CORRECT
ANSWERS 2025
gene flow correct answers >> migration of individuals
between populations
migration correct answers >> movement of individuals
(Between populations is gene flow)
Lake Erie Water Snakes overview correct answers >> on
island: banded water snakes
- snakes live on limestone rocks by the shoreline--selection for
recessive-->unbanded snakes are less visible to predators
on mainland: banded (dominant trait)
- snakes live in thick vegetation--selection for dominant-->banded
snakes are less visible to predators
-->spatially varying selection (helps maintain variation across
space in a particular species)
is a dominant/recessive allele more likely to be selectively
adventageous? correct answers >> NO
dom/rec genetic property does not tell you what will be selected
for/against
,spatially varying selection correct answers >> GET
DEFINITION
if unbanded allele favored on the island, why are there a lot of
banded snakes there? why do different islands have different
numbers of banded snakes? correct answers >> gene flow of
snakes from continent to island
why different?
habitat differences=different selection
different predators
smaller populations/size of island = drift and with smaller
population, same number of migrants would have larger impact
location - farther away = less gene flow
SELECTION+MIGRATION+(potential) DRIFT
continent-island model of migration correct answers >>
continent assumed to be large in size so amount of gene flow
back is not significant enough
tells us the frequency of the p allele on the island in the next
generation
MIGRATION ONLY ACTING
- only need to know migration rate and frequencies of this allele
on the continent and the island
,- migration rate = fraction of the island population that's arriving
from the continent each generation
Pi' = (1-m)pi+pc
pc = freq of A on continent
pi = freq of A on island
m = migration rate - fraction of island population that arrives
from the continent each generation
how to determine frequency of allele on island at equilibrium in
migration problem correct answers >> same as frequency on
island IF ONLY EVOLUTIONARY FORCE ACTING
pi=pc
migration will eventually equalize the frequencies on the island
and the continent if only acting force
if m>>s ... correct answers >> if the migration rate is higher
than the selection coefficient, migration dominates
ex: would expect to see more banded individuals on the island
if s>>m correct answers >> if selection coefficient is higher
than migration rate, selection will dominate
ex: would see mostly unbanded on island
, migration rate correct answers >> fraction of the island
population that's arriving from the continent each generation
For water snakes on islands both alleles are still present - does
this tell us something about the strength of m and s in this case?
correct answers >> intermediate frequencies
m&s are similar in magnitude
on continent, almost no unbanded so selection clearly dominant
cline correct answers >> gradual shift in a character over
space
- can often get if have balance between selection and migration
- ex: blue mussels of LI
Blue muscles example LI correct answers >> strong selection
effectively opposes migration
freq of ap94 gene increase as salinity increases
selection
- advantage at certain locus for when higher salinity
gene flow
ANSWERS 2025
gene flow correct answers >> migration of individuals
between populations
migration correct answers >> movement of individuals
(Between populations is gene flow)
Lake Erie Water Snakes overview correct answers >> on
island: banded water snakes
- snakes live on limestone rocks by the shoreline--selection for
recessive-->unbanded snakes are less visible to predators
on mainland: banded (dominant trait)
- snakes live in thick vegetation--selection for dominant-->banded
snakes are less visible to predators
-->spatially varying selection (helps maintain variation across
space in a particular species)
is a dominant/recessive allele more likely to be selectively
adventageous? correct answers >> NO
dom/rec genetic property does not tell you what will be selected
for/against
,spatially varying selection correct answers >> GET
DEFINITION
if unbanded allele favored on the island, why are there a lot of
banded snakes there? why do different islands have different
numbers of banded snakes? correct answers >> gene flow of
snakes from continent to island
why different?
habitat differences=different selection
different predators
smaller populations/size of island = drift and with smaller
population, same number of migrants would have larger impact
location - farther away = less gene flow
SELECTION+MIGRATION+(potential) DRIFT
continent-island model of migration correct answers >>
continent assumed to be large in size so amount of gene flow
back is not significant enough
tells us the frequency of the p allele on the island in the next
generation
MIGRATION ONLY ACTING
- only need to know migration rate and frequencies of this allele
on the continent and the island
,- migration rate = fraction of the island population that's arriving
from the continent each generation
Pi' = (1-m)pi+pc
pc = freq of A on continent
pi = freq of A on island
m = migration rate - fraction of island population that arrives
from the continent each generation
how to determine frequency of allele on island at equilibrium in
migration problem correct answers >> same as frequency on
island IF ONLY EVOLUTIONARY FORCE ACTING
pi=pc
migration will eventually equalize the frequencies on the island
and the continent if only acting force
if m>>s ... correct answers >> if the migration rate is higher
than the selection coefficient, migration dominates
ex: would expect to see more banded individuals on the island
if s>>m correct answers >> if selection coefficient is higher
than migration rate, selection will dominate
ex: would see mostly unbanded on island
, migration rate correct answers >> fraction of the island
population that's arriving from the continent each generation
For water snakes on islands both alleles are still present - does
this tell us something about the strength of m and s in this case?
correct answers >> intermediate frequencies
m&s are similar in magnitude
on continent, almost no unbanded so selection clearly dominant
cline correct answers >> gradual shift in a character over
space
- can often get if have balance between selection and migration
- ex: blue mussels of LI
Blue muscles example LI correct answers >> strong selection
effectively opposes migration
freq of ap94 gene increase as salinity increases
selection
- advantage at certain locus for when higher salinity
gene flow
