Transcript EVOLUTION OF POPULATIONS

CHAPTER 16
EVOLUTION OF POPULATIONS
POPULATION GENETICS
Study of evolution from a genetic point of view.
Study of the change in the GENE POOL for a
population
Example- in a garden what percent of the roses
are Red (RR), pink (Rr) or white (rr)
ALLELES
Possible traits of a gene
ALLELE FREQUENCY- how common a specific
allele is in the gene pool
PHENOTYPE FREQUENCY- how common a
specific phenotype is in a population
ALLELE FREQUENCY
ALLELE FREQUENCIES VS
PHENOTYPE FREQUENCIES
Although phenotype frequencies tend to change
generation to generation. Allele frequencies
tend to stay the same.
HARDY WEINBERG EQUILIBRUIM--p2 + 2pq + q2 = 1
HARDY WEINBERG EQUILIBRUIM1. mutation is not occurring
 2. there is no migration in or out of the
population
 3. the population is infinitely large
 4. natural selection is not occurring
 5. all members of the population breed
 6. everyone produces the same number of
offspring
 7. all mating is totally random

MUTATIONS

Can add a new allele into the mix

IMMIGRATION or EMIGRATION- can add or
subtract a bunch of individuals with one
specific allele
SMALL POPULATIONS
GENETIC DRIFT- the alelle frequency chances
simply due to chance
link to Simulation notice how the value for P will
either climb to 1 or go all the way down to 0
http://darwin.eeb.uconn.edu/simulations/drift.ht
ml
NO NATURAL SELECTION

All individuals have to have an equal chance of
survival reproduction and have the same
fitness.
RANDOM MATING (NO SEXUAL SELECTION)
NO ASSORTATIVE MATING
 All individuals must reproduce at the same
rate.

BELL CURVE OF PHENOTYPES
STABILIZING SELECTION

Individuals with the most average form of a trait
have the highest fitness

Graph– gets taller and narrower in the middle
BELL CURVE OF PHENOTYPES
DIRECTIONAL SELECTION

Individuals that have one extreme of a trait
show a higher fitness

Center of the graph moves in one direction
BELL CURVE OF PHENOTYPES
DISRUPTIVE SELECTION

Individuals at either extreme have the highest
fitness

****This can lead to one species become two
different species.

Single parabola slowly turns into 2 parabolas
BELL CURVE OF PHENOTYPES
MICROEVOLUTION VS MACROEVOLUTION

Micro-- small changes in a species

Macro- large transformations in a species
MICROEVOLUTION

is the changes in allele frequencies that occur
over time within a population. This change is
due to four different processes: mutation,
selection (natural and artificial), gene flow, and
genetic drift.
GENETIC DRIFT ----OR ALLELIC DRIFT

is the change in the frequency of a gene variant
(allele) in a population due to random
sampling.

occurs in smaller populations much faster
FOUNDER’S EFFECT

is the loss of genetic variation that occurs when
a new population is established by a very small
number of individuals from a larger population.
BOTTLENECK
a sharp reduction in size of a population due to
environmental events (such as earthquakes,
floods, fires, or droughts) or human activities.
BOTTLENECK EXAMPLES

One real life example of a species being
affected by the bottleneck effect is the
northern elephant seal. Humans intensely
hunted these animals in the late nineteenth
century, and their population was reduced to
just twenty at one point. Though the species
has recovered and there are over 30,000
northern elephant seals today, there is not a lot
of genetic diversity among members of this
species.
WHY IS A BOTTLENECK BAD?
Less genetic diversity
 More likely to reveal RECESSIVE genes

BOTTLENECK EXAMPLES
--Any ENDANGERED SPECIES
 ---Giant Panda
 --- Prairie Chicken
 --- Amish
 ---Inhabitants of small islands (Iceland)

MICROEVOLUTION BY

ISOLATION
REPRODUCTIVE ISOLATION-- individuals are
split from the rest of the population due to
some type of barrier
TYPES OF ISOLATION
 GEOGRAPHIC
ISOLATION- populations
that have been separated by physical barriers
 --Mountain ranges
 --Rivers- (Grand Canyon)
 --Ocean- (organisms separated on different
islands)
 --Human Interference ---dams, highways, fences
TYPES OF ISOLATION
BEHAVIORAL
ISOLATION– (ethological)--
- various courtship rituals or other behaviors
interfere with interbreeding
Ex- Eastern and Western Meadowlark have
different songs.
 Crickets are very species specific in their songs

TYPES OF ISOLATION
 TEMPORAL
ISOLATION-- species that
reproduce at different times
Flocks of Canadian Geese migrating at
different times
 Flowers that bloom at different times

TEMPORAL ISOLATION-
PREZYGOTIC VS POSTZYGOTIC BARRIERS

PREZYGOTIC-- prevents reproduction- (geographic, temporal,
behavioral)

POSTZYGOTIC BARRIERHybrid inviability: hybrid fails to develop or fails to reach
sexual maturity- usually due to chromosomal differences

Behavioral sterility: hybrid reaches sexual maturity but fails
to produce appropriate courtship displays or mating behavior
(plants may grow flowers that fail to attract pollinators)
Hybrid sterility: hybrids fail to produce functional gametes
MACROEVOLUTION

Large changes in a species

Rate of EVOLUTION
 1.
GRADUALISM
 2. PUNCTUATED EQUILIBRIUM
GRADUALISM

Defined as a profound change being the sum of
many slow and steady changes

Ex- ostrich wings becoming smaller and
smaller as the birds evolved.
PUNCTUATED EQUILIBRIUM

“rapid evolution” due to large changes in the
environment
Examples volcanoes forming new islands
 Small group becomes isolated
 New species enters the ecosystem

ADAPTIVE RADIATION

Single species or small group of species evolves
into several different forms
Ex- Mammals where quite small species during
the days of the dinosaur. When the dinosaurs
went extinct many species began large changes.
 (elephants, whales, rhino)
 Darwin’s finches- one species of finch turns into
many different species.
