Download IB Biology Year 2 / IHS ALTERING ALLELE FREQUENCIES KEY

IB Biology Year 2 / IHS
ALTERING ALLELE FREQUENCIES KEY
Directions: use Neil 9e sections 23.3 & 23.4 to complete this chart
Process
Description and, if appropriate, names of
different types
Predicted effect on a population’s
genetic structure
Example(s)
Mutation
Mutation, the replacement of one allele with another, is too infrequent to change p, q
Non-random mating
Non-random mating, the choosing of partners by particular phenotypes, does not change p and q, only genotype frequencies.
Natural selection
Differential success in survival
and reproduction. The result,
usually, is that NS matches
organisms to their environments.
Directional selection: pop. mean shifts one
direction or the other. If this occurs in several
populations beginning from one gene pool, it is
known as ADAPTIVE RADIATION.
Disruptive selection: acquisition of bimodal
population.
May change p, q
Stabilizing selection: the most common
phenotype is the most selected for; at work all
the time, everywhere.
May change p, q
Sexual selection: Female choice (usually) selects
for an exaggerated trait in males. (Why?
Probably association with health!)
May change p, q
Founder Effect: colonization, when a small part
of the population breaks off from the rest; likely
the colonists’ gene pool is different from that of
the source population.
May change p, q or even lose alleles
due to chance
Bottleneck: when a population experiences a
natural disaster (unrelated to pop. members'
genetics) or other event that reduces its size at
some point.
May change p, q or even lose alleles
due to chance, thus reducing genetic
variation; in subsequent pop’s; can
also fix alleles.
Remember, NS won’t cull all
unfavorable alleles:
it doesn’t “see”
recessive alleles in a
heterozygote,
sometimes
heterozygotes are most
fit, which maintains
recessive alleles in the
pop.
Sometimes NS is
frequency dependent,
so the fitness of a
phenotype depends on
how common it is.
Genetic drift
= Chance events causing p & q to
fluctuate unpredictably, even
sometimes losing genetic
variation
May change p, q
Galapagos finch beaks as a result of
drought affecting type of seed
available; Drosophila resistance to
insecticides like DDT
Patchy environments, like gold mice
on sand and black mice on lava
flows; or seed cracker finches in
Cameroon
Human birth weight: very small and
very large babies experience
increased mortality relative to
“average” sized babies.
A male peacock’s bright feathers.
NOTE: his big, gaudy feathers do
not confer a survival advantage but
if peahens choose him to mate,
that’s what counts!
RP in human pop. on Tristan de
Cunha, a British island in the
Atlantic. All people descended from
original group of 15, one of which
carried RP allele
Greater prairie chicken pop’s in
Illinois, modern vs. museum
specimens, and vs. KS and NE flocks
– fewer alleles per locus.
Gene flow
Transfer of alleles in/out of a population due to
movements of fertile individuals or their
gametes
Increases genetic variation within a
pop, but reduces it between pop’s.
May be the result of incomplete
reproductive isolation.
Two songbird pop’s on Dutch island
of Vlieland; the central population
has gene flow with mainland pop,
bringing untested alleles. Eastern
population has less gene flow and is
therefore more adapted to island
conditions.