Transcript Dispatch - Cloudfront.net

Dispatch—Explain this
cladogram
Practice Evolution Quiz
• http://tinyurl.com/3nmb6gm
Problem 3
• If you observe a population and find that
16% show the recessive trait, you know
the frequency of the aa genotype. This
means you know q2. What is q for this
population?
Evolution of populations
• Evolution = change in allele frequencies
in a population
– hypothetical: what conditions would cause
allele frequencies to not change?
– non-evolving population
REMOVE all agents of evolutionary change
1. very large population size (no genetic drift)
2. no migration (no gene flow in or out)
3. no mutation (no genetic change)
4. random mating (no sexual selection)
5. no natural selection (everyone is equally fit)
5 Agents of evolutionary change
Gene Flow
Genetic Drift
Mutation
Non-random mating
Selection
Application of H-W principle
• Sickle cell anemia
– inherit a mutation in gene coding for
hemoglobin
• oxygen-carrying blood protein
• recessive allele = HsHs
– normal allele = Hb
– low oxygen levels causes
RBC to sickle
• breakdown of RBC
• clogging small blood vessels
• damage to organs
– often lethal
Sickle cell frequency
• High frequency of heterozygotes
– 1 in 5 in Central Africans = HbHs
– unusual for allele with severe
detrimental effects in homozygotes
• 1 in 100 = HsHs
• usually die before reproductive age
Why is the Hs allele maintained at such high
levels in African populations?
Suggests some selective advantage of
being heterozygous…
Single-celled eukaryote parasite
Malaria
(Plasmodium) spends part of its
life cycle in red blood cells
1
2
3
Heterozygote Advantage
• In tropical Africa, where malaria is common:
– homozygous dominant (normal)
• die or reduced reproduction from malaria: HbHb
– homozygous recessive
• die or reduced reproduction from sickle cell anemia: HsHs
– heterozygote carriers are relatively free of both: HbHs
• survive & reproduce more, more common in population
Hypothesis:
In malaria-infected
cells, the O2 level is
lowered enough to
cause sickling which
kills the cell & destroys
the parasite.
Frequency of sickle cell allele
& distribution of malaria
Hardy-Weinberg lab pod cast
• http://www.youtube.com/watch?v=KmqgZv
Uoq3k
Lab—Part A
Taster
NonTaster
PTC
Control
Non-Tasters=Homo recessive (aa)
Tasters=Homo Dominant (AA) or Heter (Aa)
Figure out the p2 and 2pq for our class
Results and Discussion
• 5 Hardy Weinberg calculations
• Show work—organzied part A-E
• Discussion: In part A evolution did/did not
happen because…. In part B…. In part C
• Explain WHY, use terms
Part B—Testing an ideal Population
Initial Class Frequencies GG____ Gg____ gg___
My initial genotype ___
F1____
F2_____
F3_____
F4_____
F5______
Final Class Frequencies
GG____ Gg____ gg ___
Part C—Selection (homo recessive
selected against)
Initial Class Frequencies GG____ Gg____ gg___
My initial genotype ___
F1____
F2_____
F3_____
F4_____
F5______
Final Class Frequencies
GG____ Gg____ gg___
Part D—Heterozygous Advantage
(Homo dom—may die of maleria (flip coin; homo
recessive—die of sickle cell)
• Initial Class Frequencies GG____ Gg 24/48
gg___
• My initial genotype ___
• F1____
• F2_____
• F3_____
• F4_____
• F5______
Final Class Frequencies
• GG 16/48 Gg 32/48 gg 0/48
Part E—Genetic Drift (break into 3
smaller populations—make
hypothesis)
• Initial Class Frequencies GG____ Gg____
gg___
• My initial genotype ___
• F1____
• F2_____
• F3_____
• F4_____
• F5______
Final Class Frequencies
Frequencies GG____ Gg____ gg___
Macroevolution: the origin of new taxonomic groups
•
•
Speciation: the origin of new species
1- Anagenesis (phyletic evolution): accumulation
of heritable changes
•
2- Cladogenesis (branching evolution):
budding of new species from a parent species that
continues to exist (basis of biological diversity)
What is a species?
• Biological species concept
(ErnstMayr): a population or group of
populations whose members have the
potential to interbreed and produce viable,
fertile offspring (genetic exchange is
possible and that is genetically isolated
from other populations)
How and why do new species originate?
• Species are created by a series of
evolutionary processes
– populations become isolated
• geographically isolated
• reproductively isolated
– isolated populations
evolve independently
Dispatch—Draw and explain
Modes of speciation
(based on how gene flow is interrupted)
• Allopatric: “other country”
populations segregated by a
geographical barrier; can result in
adaptive radiation (island species)
• Sympatric: “same country
reproductively isolated
subpopulation in the midst of its
parent population (change in
genome); polyploidy in plants;
cichlid fishes
Reproductive Isolation (isolation of gene pools), I
•
•
•
•
•
•
Prezygotic barriers: impede mating between
species or hinder the fertilization of the ova
Habitat (snakes; water/terrestrial)
Behavioral (fireflies; mate signaling)
Temporal (salmon; seasonal mating)
Mechanical (flowers; pollination anatomy)
Gametic (frogs; egg coat receptors)
Habitat isolation
• Species occur in same region, but occupy different habitats so rarely
encounter each other
– reproductively isolated
2 species of garter snake, Thamnophis, occur in
same area, but one lives in water & other is
terrestrial
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lions & tigers could
hybridize, but they live
in different habitats:
 lions in grasslands
 tigers in rainforest
Temporal isolation
• Species that breed during different times of day, different seasons, or
different years cannot mix gametes
– reproductive isolation
Eastern spotted skunk (L)
& western spotted skunk
(R) overlap in range but
eastern mates in late
winter & western mates in
late summer
Behavioral isolation
• Unique behavioral patterns & rituals isolate species
– identifies members of species
– attract mates of same species •
• courtship rituals, mating calls
• reproductive isolation
Blue footed boobies mate only
after a courtship display unique
to their species
sympatric speciation?
Mechanical isolation
• Morphological differences can prevent successful mating
– reproductive isolation
Plants
Even in closely related species
of plants, the flowers often
have distinct appearances that
attract different pollinators.
These 2 species of monkey
flower differ greatly in shape &
color, therefore crosspollination does not happen.
Mechanical isolationAnimals
• For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer
– lack of “fit” between sexual organs:
hard to imagine for us… but a big issue for insects with different shaped genitals!
Damsel fly penises
Gametic isolation
• Sperm of one species may not be able to fertilize eggs of another
species
– mechanisms
• biochemical barrier so sperm cannot penetrate egg
– receptor recognition: lock & key between egg & sperm
• chemical incompatibility
– sperm cannot survive in female reproductive tract
Sea urchins release sperm &
eggs into surrounding waters
where they fuse & form
zygotes. Gametes of different
species— red & purple —are
unable to fuse.
Gametic isolation
• Sperm of one species may not be able to fertilize eggs of another
species
– mechanisms
• biochemical barrier so sperm cannot penetrate egg
– receptor recognition: lock & key between egg & sperm
• chemical incompatibility
– sperm cannot survive in female reproductive tract
Sea urchins release sperm &
eggs into surrounding waters
where they fuse & form
zygotes. Gametes of different
species— red & purple —are
unable to fuse.
Reproductive Isolation, II
•
•
•
•
Postzygotic barriers: fertilization occurs, but the
hybrid zygote does not develop into a viable, fertile
adult
Reduced hybrid viability (frogs; zygotes fail to
develop or reach sexual maturity)
Reduced hybrid fertility (mule; horse x donkey;
cannot backbreed)
Hybrid breakdown (cotton; 2nd generation
hybrids are sterile)
Reduced hybrid viability
• Genes of different parent species may
interact & impair the hybrid’s development
Species of salamander
genus, Ensatina, may
interbreed, but most
hybrids do not complete
development & those that
do are frail.
Reduced hybrid fertility
• Even if hybrids are vigorous
they may be sterile
– chromosomes of parents may differ in number or structure & meiosis in
hybrids may fail to produce normal gametes
Mules are vigorous,
but sterile
Horses have 64
chromosomes
(32 pairs)
Mules have 63 chromosomes!
Donkeys have 62
chromosomes
(31 pairs)
Hybrid breakdown
• Hybrids may be fertile & viable in first
generation, but when they mate offspring
are feeble or sterile
In strains of cultivated rice,
hybrids are vigorous but plants
in next generation are small &
sterile.
On path to separate species.