Transcript Evolution & Speciation

EVOLUTION &
SPECIATION
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
Gene Pool
Combined genetic
info. of all
members
Allele frequency is
# of times
alleles occur
Variation in Populations
2 processes can
lead to this:
Mutations change in DNA
sequence
Gene Shuffling –
from sexual
reproduction
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: inbreeding and
assortive mating (both shift
frequencies of different genotypes)
• 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
Evolution of Populations
Occurs when there
is a change in
relative
frequency of
alleles
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
Allele Frequencies
Natural Selection
Single Gene
Traits
Genetic Drift
Polygenic
Traits
Directional
Selection
Stabilizing Selection
Disruptive Selection
Conditions needed for Genetic
Equilibrium
SPECIATION
• THE FORMATION OF NEW SPECIES
• AS NEW SPECIES EVOLVE,
POPULATIONS BECOME
REPRODUCTIVELY ISOLATED
• REPRODUCTIVE ISOLATION –
MEMBERS OF 2 POPULATIONS
CANNOT INTERBREED & PRODUCE
FERTILE OFFSPRING.
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
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 are infertile.
Table 23.1b
These squirrels live on opposite sides of the Grand
Canyon. This is an example of allopatric speciation.