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

Mutation

Gene FlowGenetic Drift

Selection

Non-random mating

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?Why is the Hs allele maintained at such high levels in African populations?

Suggests some selective advantage of being heterozygous…Suggests some selective advantage of being heterozygous…

Malaria Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells

Single-celled eukaryote parasite (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.

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=KmqgZvUoq3k

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 FrequenciesGG____ 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 FrequenciesGG____ 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 FrequenciesFrequencies GG____ Gg____ gg___

Macroevolution: Macroevolution: the origin of new taxonomic groupsthe origin of new taxonomic groups

• Speciation: Speciation: the origin of new speciesthe origin of new species

• 1-1- Anagenesis Anagenesis (phyletic evolution): (phyletic evolution): accumulation of heritable changesaccumulation 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?What is a species?

• Biological species concept Biological species concept

(ErnstMayr):(ErnstMayr): a population or group of a population or group of populations whose members have the populations whose members have the potential to interbreed and produce viable, potential to interbreed and produce viable, fertile offspring (genetic exchange is fertile offspring (genetic exchange is possible and that is genetically isolated possible and that is genetically isolated from other populations)from other populations)

How and why do new species originateHow and why do new species originate??

• Species are created by a series of Species are created by a series of evolutionary processesevolutionary processes– populations become populations become isolatedisolated

• geographically isolated geographically isolated • reproductively isolatedreproductively isolated

– isolated populations isolated populations evolve independentlyevolve independently

Dispatch—Draw and explainDispatch—Draw and explainModes of speciation Modes of speciation

(based on how gene flow is interrupted)(based on how gene flow is interrupted)

• AllopatricAllopatric:: “other country”“other country” populations segregated by a populations segregated by a geographical barrier; can result in geographical barrier; can result in adaptive radiation (island species)adaptive radiation (island species)

• SympatricSympatric:: ““samesame countrycountry reproductively isolated reproductively isolated subpopulation in the midst of its subpopulation in the midst of its parent population (change in parent population (change in genome); polyploidy in plants; genome); polyploidy in plants; cichlid fishescichlid fishes

Reproductive Isolation (isolation of gene pools), IReproductive Isolation (isolation of gene pools), I

• Prezygotic barriers:Prezygotic barriers: impede mating between impede mating between species or hinder the fertilization of the ovaspecies or hinder the fertilization of the ova

• Habitat (snakes; water/terrestrial)Habitat (snakes; water/terrestrial)• Behavioral (fireflies; mate signaling)Behavioral (fireflies; mate signaling)• Temporal (salmon; seasonal mating)Temporal (salmon; seasonal mating)• Mechanical (flowers; pollination anatomy)Mechanical (flowers; pollination anatomy)• Gametic (frogs; egg coat receptors)Gametic (frogs; egg coat receptors)

Habitat isolationHabitat isolation• Species occur in same region, but occupy different habitats so Species occur in same region, but occupy different habitats so rarelyrarely

encounter each otherencounter each other– reproductively isolatedreproductively isolated

2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

lions & tigers could hybridize, but they live in different habitats: lions in grasslands tigers in rainforest

lions & tigers could hybridize, but they live in different habitats: lions in grasslands tigers in rainforest

Temporal isolationTemporal isolation• Species that breed during different times of day, different seasons, or Species that breed during different times of day, different seasons, or

different years cannot mix gametesdifferent years cannot mix gametes– reproductive isolationreproductive isolation

Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

Behavioral isolationBehavioral isolation• Unique behavioral patterns & rituals isolate speciesUnique behavioral patterns & rituals isolate species

– identifies members of species identifies members of species – attract mates of same species attract mates of same species ��

• courtship rituals, mating callscourtship rituals, mating calls• reproductive isolationreproductive isolation

Blue footed boobies mate only after a courtship display unique to their species

Blue footed boobies mate only after a courtship display unique to their species

Mechanical isolationMechanical isolation

• Morphological differences can prevent successful matingMorphological differences can prevent successful mating– reproductive isolationreproductive isolation

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 cross-pollination does not happen.

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 cross-pollination does not happen.

Plants

sympatric speciation?

Mechanical isolationMechanical isolation

• For many insects, male & For many insects, male & female sex organs of female sex organs of closely related species do closely related species do not fit together, preventing not fit together, preventing sperm transfersperm transfer– lack of “fit” between sexual organs: lack of “fit” between sexual organs:

hard to imagine for us… but a big issue for insects with different shaped genitals!hard to imagine for us… but a big issue for insects with different shaped genitals!

Damsel fly penises

Animals

Gametic isolationGametic isolation• Sperm of one species may not be able to fertilize eggs of another Sperm of one species may not be able to fertilize eggs of another

speciesspecies– mechanismsmechanisms

• biochemical barrierbiochemical barrier so sperm cannot penetrate egg so sperm cannot penetrate egg– receptor recognition: lock & key between egg & spermreceptor recognition: lock & key between egg & sperm

• chemical incompatibilitychemical incompatibility – sperm cannot survive in female reproductive tractsperm 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.

Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

Gametic isolationGametic isolation• Sperm of one species may not be able to fertilize eggs of another Sperm of one species may not be able to fertilize eggs of another

speciesspecies– mechanismsmechanisms

• biochemical barrierbiochemical barrier so sperm cannot penetrate egg so sperm cannot penetrate egg– receptor recognition: lock & key between egg & spermreceptor recognition: lock & key between egg & sperm

• chemical incompatibilitychemical incompatibility – sperm cannot survive in female reproductive tractsperm 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.

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, IIReproductive Isolation, II

• Postzygotic barriersPostzygotic barriers: : fertilization occurs, but the fertilization occurs, but the hybrid zygote does not develop into a viable, fertile hybrid zygote does not develop into a viable, fertile adultadult

• Reduced hybrid viability (frogs; zygotes fail to Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity)develop or reach sexual maturity)

• Reduced hybrid fertility (mule; horse x donkey; Reduced hybrid fertility (mule; horse x donkey; cannot backbreed)cannot backbreed)

• Hybrid breakdown (cotton; 2nd generation Hybrid breakdown (cotton; 2nd generation hybrids are sterile)hybrids are sterile)

Reduced hybrid viabilityReduced hybrid viability• Genes of different parent species may Genes of different parent species may

interact & impair the hybrid’s developmentinteract & impair the hybrid’s development

Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

Mules are vigorous, but sterile

Reduced hybrid fertilityReduced hybrid fertility

• Even if hybrids are vigorous Even if hybrids are vigorous they may be sterilethey may be sterile– chromosomes of parents may differ in number or structure & meiosis in chromosomes of parents may differ in number or structure & meiosis in

hybrids may fail to produce normal gameteshybrids may fail to produce normal gametes

Donkeys have 62 chromosomes(31 pairs)

Horses have 64 chromosomes(32 pairs) Mules have 63 chromosomes!

Hybrid breakdownHybrid breakdown• Hybrids may be fertile & viable in first Hybrids may be fertile & viable in first

generation, but when they mate offspring generation, but when they mate offspring are feeble or sterileare feeble or sterile

In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.On path to separate species.

In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.On path to separate species.