Transcript GEOGRAPHICAL ISOLATION

Evidence of Evolution
1. Fossil Record
2. Geographic Distribution of Living
Species
3. Anatomical similarities
- homologous Body structures
4. Similarities in Embryology
5. The more closely related, the more
similarities in DNA.
January 19/20, 2012
• Quiz
• Mechanics of Evolution lecture
• Natural Selection
Lab
• Be sure other labs
are ready to turn
in.
Mechanisms of
EVOLUTION
VOCABULARY REVIEW
• EVOLUTION – CHANGE OVER TIME
• NATURAL SELECTION - INDIVIDUALS
BETTER ADAPTED TO THE
ENVIRONMENT ARE ABLE TO
SURVIVE & REPRODUCE.
– A.K.A. “SURVIVAL OF THE FITTEST”
NEW VOCABULARY
• POPULATION – GROUP OF
INDIVIDUALS OF SAME SPECIES
THAT INTERBREED
• GENE POOL – COMMON GROUP OF
ALL GENES PRESENT IN A
POPULATION
Variation in Populations
2 processes can
lead to this:
Mutations change in DNA
sequence
Gene Shuffling –
from sexual
reproduction
Gene Pool
Combined genetic
info. of all
members
Allele frequency is
# of times
alleles occur
Genetic Drift changes populations…….
• Random change in allele
frequency causes an allele to
become common
• Founder Effect:
a cause of genetic
drift attributable to
colonization by a
limited number of
individuals from a
parent population
• Gene Flow:
genetic exchange
due to the
migration of fertile
individuals or
gametes between
populations
(reduces
differences
between
populations)
• Nonrandom mating aka artificial
selection: inbreeding and assortive
mating (both shift frequencies of
different genotypes)
Evolution of Populations
Occurs when there is a
change in relative
frequency of
alleles……….
in other words – a
change in the
contents of the gene
pool
• Natural Selection:
differential
success in
reproduction;
only form of
microevolution
that adapts a
population to its
environment
Sexual selection
• Sexual
dimorphism:
secondary sex
characteristic
distinction
• Sexual selection:
selection towards
secondary sex
characteristics
that leads to
sexual
dimorphism
Phenotype Expression
• Depends on
how many
genes control
that trait
Single-Gene vs. Polygenic Traits
Single-Gene:
2 Distinct Phenotypes (EG: tongue rolling)
Polygenic:
Many Phenotypes
Natural Selection on Polygenic Traits
• Shifts to
middle range
• Shifts to
2 extremes
• Shifts to
1 extreme
Allele Frequencies
Natural Selection
Single Gene
Traits
Genetic Drift
Polygenic
Traits
Directional
Selection
Stabilizing Selection
Disruptive Selection
SPECIATION
THE FORMATION OF NEW SPECIES
• AS POPULATIONS ARE ISOLATED , THEY
BECOME REPRODUCTIVELY ISOLATED
• REPRODUCTIVE ISOLATION – MEMBERS OF
2 POPULATIONS CANNOT INTERBREED &
PRODUCE FERTILE OFFSPRING.
• REPRODUCTIVE ISOLATION LEADS TO
SPECIATION
3 ISOLATING MECHANISMS……..
• BEHAVIORAL ISOLATION- CAPABLE OF
BREEDING BUT HAVE DIFFERENCES IN
COURTSHIP RITUALS (EX.
MEADOWLARKS)
• GEOGRAPHICAL ISOLATION –
SEPARATED BY GEOGRAPHIC BARRIERS
LIKE RIVERS, MOUNTAINS, OR BODIES
OF WATER (EX. SQUIRREL)
• TEMPORAL ISOLATION – 2 OR MORE
SPECIES REPRODUCE AT DIFFERENT
TIMES.
Table 23.1a
Fig. 23.6
Four species of leopard frogs: differ in their
mating calls. Hybrids are inviable.
These squirrels live on opposite sides of the Grand
Canyon. This is an example of allopatric speciation.
Hawaiian Honeycreepers
An example of adaptive radiation –
these species all diverged from a
common ancestor (founder species)
FOUNDER SPECIES
SPECIATION IN DARWIN’S
FINCHES
• SPECIAITON IN THE GALAPAGOS
FINCHES OCCURRED BY:
- FOUNDING OF A NEW POPULATION,
- GEOGRAPHIC ISOLATION which led to - REPRODUCTIVE ISOLATION and
CHANGES IN THE NEW POPULATION’S
GENE POOL due to COMPETITION.
Table 23.1b
Tigon
Result of male tiger
and female lion
mating incaptivity.
Offspring are infertile.
Separated both
geographically and
ecologically.
Liger
Result of male lion and female
tiger mating in captivity.
Offspring may be infertile.
http://www.youtube.com/watch?v=7dx2CUMtZ-0&feature=related
http://www.youtube.com/watch?v=OmLgbY8gBN8
http://www.youtube.com/watch?v=UpoGfbQ0l8o&feature=related
http://www.youtube.com/watch?v=eI_quJRRGxk&feature=related
Conditions needed for Genetic
Equilibrium