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In speciation lies the __________________________, and the study of speciation bridges ___________________________

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origin of diversity microevolution and macroevolution

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Evolution of diversity occurs by

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cladogenesis anagenesis

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cladogenesis

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branching of lineages

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anaenesis

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evolution within a species

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Speciation Time Long process to be observed by _________________________ of scientists

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one or a few generations

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Speciation Time too ___________________________ to find it well documented in the fossil record

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short for geological time scales

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Species - latin for "_______"

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kind

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What is a Species Highly dependent on

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the context of the definition used

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Species can be defined to #1

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Enable us to classify organisms

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Species can be defined to #2

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Correspond to discrete groups of similar organisms

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Species can be defined to #3

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Help us understand how discrete clusters of organisms arise in nature

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Species can be defined to #4

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Represent products of evolutionary history

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Species can be defined to #5

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Apply to the largest possible variety of organisms

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No two of these possible goals always coincide thus it is unlikely that

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any one species concepts will serve most of these purposes

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The Crow Story The two european crows look more different from one another than crows do from ravens - however there is

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a clear hybrid zone between the carrion crow and the hooded crow

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Species Concepts

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biological evolutionary phylogenetic genealogical cohesion

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Biological Species Concept (BSC) Mayr (1942) - "Species are groups of actually or potentially interbreeding natural populations that are ___________________________ from other such groups"

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reproductively isolated

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Phylogenetic Species Concept (PSC) Cracraft (1989) - "An irreducible (basal) cluster of organisms that is diagnosably distinct from other such clusters, and within which there is a ___________________________________________". Applies to _________________________ organisms

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parental pattern of ancestry and descent sexual and asexual

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Phylogenetic Species Concept (PSC) de Queiroz and Donaghue (1990) - "The _________________________ of common ancestry"

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smallest monophyletic group

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Evolutionary Species Concept (ESC) Wiley (1978) - "A species is a ___________________________ that maintains an identity separate from other such lineages and which has its ________________________".

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single lineage of populations own evolutionary fate

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Most widely used species concepts today:

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Biological Species Concept Phylogenetic Species Concept

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_____________________________________ emphasizes species as the outcome of evolution, the products of divergence

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Phylogenetic Species Concept

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_____________________________________ emphasizes the process by which species arise

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Biological Species Concept

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Regardless of which concept is used, some populations will not be

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unambiguosly assigned to one species or another

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Most frequently used by evolutionary biologists concerned with process

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Biological Species Concept

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"Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups".

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Biological Species Concept

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Biological Species Concept Reproductive isolation means that biological differences between populations ___________________________ even in the absence of geographic isolation

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reduce gene exchange

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Biological Species Concept Advocates of BSC recognize that there can be some _________________________.

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gene exchange "leakage"

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Development of the Biological Species Concept

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variation within populations

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Development of the Biological Species Concept - Variation Within Populations White and blue color morphs of the snow goose from the same mother represent _________________________.

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a genetic polymorphism

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Development of the Biological Species Concept Geographic Variation

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human populations

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Development of the Biological Species Concept Sibling species are _________________________ but _____________________ ____________________.

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reproductively isolated indistinguishable morphologically

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Development of the Biological Species Concept Sibling species are reproductively isolated but indistinguishable morphologically. Recognized by differences in

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ecology, behavior, chromosomal number

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Some Terms Used in the Species Literature

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geographic isolation reproductive isolation

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Geographic Isolation Reduction/prevention of gene flow between populations by

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an extrinsic barrier to movement

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Reproductive Isolation Prevention of gene flow by

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genetically determined differences

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Terms Used in the Species Literature Population Types

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Allopatric Parapatric Sympatric

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Allopatric Population

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located in separate geographic areas

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Parapatric Populations

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adjacent, meeting at the border

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Sympatric Population

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in the SAME location

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Sibling Species

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reproductively isolated but difficult to distinguish morphologically

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Sister Species

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derived from an immediate common ancestor

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Hybrid Zone

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region where genetically distinct populations interbreed to some extent

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Introgression

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movement of genes from one distinct population into another

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Semispecies

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parapatric populations nearly but not quite different species

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Fitness

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reproductive success

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Pleiotropy

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multiple effects of a single gene

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Epistasis when the action of one gene is modified by one or more others that assort __________________________ (i.e. the two genes may be quite tightly linked, but their effects must reside at __________________________)

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somewhat independently different loci in the genome

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Restricted to sexual, outcrossing organisms as well as short intervals (not useful in long geologic time intervals)

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Domain of Biological Species Concept

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Borderline Cases Hybrid Zones

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example of sympatric hybridization in oaks

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Borderline Cases Geographic Variation in Status

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genetically different populations or conspecific in certain areas and different species elsewhere

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Difficulty of Biological Species Concept assessing if allopatric populations belong to the same species since

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it requires assessment of potential interbreeding

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Conflict between Phylogenetic Species Concept and Biological Species Concept

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in classification

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Conflict between Phylogenetic Species Concept and Biological Species Concept In Classification - distinct allopatric populations would be considered species by the _______ but if the differences were only slight they would be considered

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PSC variants of the same species under the BSC

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Conflict between Phylogenetic Species Concept and Biological Species Concept In Classification - when making trees with new species, the PSC would require

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renaming old species while the BSC would consider one paraphyletic

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Gene Flow Barriers aka

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isolating mechanisms isolating barriers

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Gene Flow Barriers under the BSC speciation consists of

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the evolution of biological barriers to gene flow

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Premating Barriers Ecological Isolation

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different breeding seasons habitat isolation

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Premating Barriers Behavioral Isolation

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sexual isolation

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Premating Barriers Behavioral Isolation (Sexual Isolation) Important among ______________ __________

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sympatric species

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Premating Barriers Behavioral Isolation (Sexual Isolation) Specific Mate Recognition Signals

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signals and responses between potential mates one sex will not respond to inappropriate signals

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Behavioral Isolation Morphologically indistinguishable insect species with ___________________________. Females discriminate against ____________________________.

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distinct mating songs other species as well as hybrids

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Behavioral Isolation Visual signals are often used in combination with __________________________ signals in courtship behavior

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chemical and acoustic

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Plants Behavioral isolation does not exist per se. Different pollinating animals respond to differences in

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color, form or scent

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Postmating Prezygotic Barriers

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conspecific sperm precedence gametic isolation

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Conspecific Sperm Precedence

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insects and pollinated plants

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Gametic Isolation

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important in free spawning marine invertebrates

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Orbicella species complex __________ sibling species

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three

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Orbicella species complex combination of premating and postmating barriers

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different spawning times lower hybrid viability

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Population Collapse in Early Pleisocene

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mass extinction of Orbicella species between 1 and 2 Mya share evolutionary history for all species until 700 ky

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Postzygotic Barriers

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hybrid inviability hybrids sterility

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Postzygotic Barriers Hybrid Inviability

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hybrids have LOWER survival rates than nonhybrids

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Postzygotic Barriers Hybrid Sterility

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differences between the genes from two parents

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Hybrid Sterility Structural differences between the ______________ producing gametes with an __________________________ of chromosomes

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chromosomes unbalanced complement

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Haldane's Rule Hybrid sterility is limited to the heterogametic sex →

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the one with two different chromosomes MALES in mammals, insects FEMALES in birds, butterflies

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Hybrid Sterility is manifested in

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F1, F2 and backcross offspring

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In Drosophila, both prezygotic and postzygotic isolation increases gradually with time since

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the separation of populations (speciation is gradual)

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Prezygotic isolation measured by

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mating success (or failure)

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Postzygotic isolation measured by

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survival and fertility of hybrids

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In Drosophila, prezygotic isolation is STRONGER among

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sympatric than among allopatric pairs of taxa

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Genetic Basis of Reproductive Barriers Hybrid Sterility measured by

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sperm motility

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Genetic Basis of Reproductive Barriers Every chromosome arm derived from D.mauritania had ____________ sperm motility compared to D. simulans

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reduced

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Epistasis Interactions between genes that contribute to hybrid sterility do NOT have

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the same interactions in the two parent species

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Ancestral Species ↓ Independent Divergence ↓ Deleterious interactions in hybrids ↓ hybrid ________________

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inviable because the genes have diverged in the two species

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Early acquisition of hybrid sterility requires

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few gene differences

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The X chromosome has

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a GREATER effect than any autosome

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Genes that cause reproductive isolation are

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poorly known

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one of the best known examples of genes that cause reproductive isolation

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Nup96

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Nup96 Encodes for a _____________ protein in the nuclear pore complexes which regulate passage between _____________________________

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nucleoporin cell nucleus and cytoplasm

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Chromosomes & Isolation Reciprocal Translocation

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can cause aneuploidy (abnormal numbers of specific chromosomes)

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Chromosomes & Isolation In Animals - chromosomal heterozygotes have __________ fitness probability due to aneuploidy

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LOWER mole rats in Israel

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Dobzhansky-Muller Incompatibility Reproductive isolation is usually due to

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differences in multiple loci

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Dobzhansky-Muller Incompatibility Reproductive isolation requires populations/species

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diverge by at least two allele substitutions

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Dobzhansky-Muller Incompatibility AABB (ancestral) ↓ ↓

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AAbb aaBB (derived) (derived) a and b are incompatible AaBb are low fitness hybrids

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Coalescence A population with two alleles at time 0 - by chance

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(genetic drift) some individuals fail to leave descendants

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Coalescence At time t all copies of a gene are descended from a single ancestral gene copy - they

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coalesce back to a single common ancestor

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Coalescence Lineage sorting is ____________ in smaller populations

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FASTER

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Lineage Sorting

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when the gene tree reflects the species tree

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Ancestral Polymorphisms

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often shared in closely related species lineage sorting is incomplete

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Lake Malawi's cichilds Branches

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haplotypes

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Lake Malawi's cichilds Color Acronyms

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different species with same haplotype

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Hybrid Zone by

answer

divergent selection secondary contact

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Yellow Bellied Toads

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secondary contact

Evolution – Exam #4 – Species – Flashcards

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