DOC PREVIEW
UCSB EEMB 2 - Lec #14 EEMB 2 SM17 1S (Genetic Divergence Reproductive Isolation)

This preview shows page 1-2-3-4-5 out of 16 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

The Evolutionary process:1. Variation2. Natural Selection 3. Genetic Divergence4. Reproductive Isolation5. SpeciationVariationNatural SelectionReproductive isolationGenetic DivergenceSpeciationGenetic DivergenceGenetic DivergenceGene Flow: The physical movement of alleles into & out of a population through immigration and emigration 1. alleles are lost from a population via emigration2. alleles enter a population via immigration - the physical flow of alleles (gene flow) tends to counter genetic differences - can slow a population from fully adapting to new environments - common way to introduce new alleles to a populationEx: human populations, blue jaysGenetic DivergenceGenetic drift: The random change in allele frequencies over the generations, brought about by chance.1. Changes in allele frequencies due to genetic drift occur regardless of the fitness of individuals (Chance).2. Genetic drift either favors the elimination or fixation of an allele (0% or 100%)Sampling error: the smaller the sample size, the greater the chance of deviation from predicted results (applies every time random mating & fertilization take place in a pop.)In natural populations:Genetic drift tends to reduce genetic variation and leads to the homozygous conditiondeviations from expected results because Real populations are finite in size (small sample size)Genetic DivergenceGenetic drift: 2 situations that increase the impact of genetic drift on a population & rapidly alter allelic frequenciesThe bottleneck effect: A severe reduction in population size brought about by intense selection pressure or natural disasterEx: contagious disease, habitat loss, hunting, volcanoes, etc.Disruptive selectionOriginal populationNew populationGenetic DivergenceThe Bottleneck Effect: 1. Survivors gene pool may no longer represent the original population2. By chance certain alleles may be over represented, under represented or eliminated 3. Genetic drift may continue to alter the gene pool & reduce variation when the population size is smallEx: Elephant seals (severe hunting resulted in bottleneck, & a reduction in variation)Ex: Cheetah (monomorphic for many genes)Genetic DivergenceThe Founders Effect: When a few individuals become isolated from a larger pop.1. Occurs when a few members migrate to a new habitat (establish a new population in a new habitat)2. isolated gene pool may no longer represent the original populationEx: Isolated islandsIn the absence of gene flow, natural selection will alter allele frequencies in different ways due to genetic driftMigrationOriginal populationNew populationGenetic DivergenceGenetic divergence: Any structural, functional or behavioral difference that favors reproductive isolation is a by product of genetic change1. Genetic changes between populations can be countered by gene flow (homogenizes genetic differences)2. Barriers prevent the exchange of genes between populations and leads to evolutionary divergence of each populationGenetic divergence leads to differences between gene pools of the separate populations (mutation, natural selection, genetic drift)TimeParent speciesDaughter speciesbarrierWestern MeadowlarkEastern MeadowlarkThe Evolutionary process:1. Variation2. Natural Selection 3. Genetic Divergence 4. Reproductive Isolation5. SpeciationVariationNatural SelectionReproductive isolationGenetic DivergenceSpeciationReproductive Isolating MechanismsReproductive Isolating MechanismsReproductive Isolating Mechanisms: Any heritable feature of body form, function, or behavior that prevents interbreeding between one or more genetically divergent populations - RIMs result as a by-product of genetic divergence- Maintains positive adaptations for specific environmentsTypes of reproductive isolating mechanisms:1. Prezygotic isolating mechanisms(mechanisms of isolation before or during fertilization)2. Postzygotic isolating mechanisms(mechanisms of isolation after fertilization)Reproductive Isolating MechanismsPrezygotic Isolation:1. Ecological isolation: Isolation due to adaptation to different microclimates in the same habitatEx: California Oaks (Santa Ynez Valley) - 3 species1. valley oak (Quercus lobata)2. live oak (Quercus agrifolia)3. shrub oak (Quercus dumosa)Separation is based on physiological mechanisms to promote conservation of waterQuercus lobataQuercus agrifoliaQuercus dumosaReproductive Isolating MechanismsPrezygotic Isolation:2. Geographic isolation: Isolated by distance or geographic barriers (Do not come in contact) - distance or barrier relative to the size of the organismEx: Louse (lice) 2 subspecies1. head lice (Pediculus humanus var. capitis) 2. body lice ( Pediculus humanus var. vestimenti) Geographic isolation is the hairless region of the neckReproductive Isolating MechanismsPrezygotic Isolation:3. Temporal isolation: Isolated by reproductive events that occur at different times (mating, flowering days or seasons do not overlap)Ex: Cicadas (Magicidada) - 3 species- insect mature underground, reproduce every 17 years- each species has sibling species, reproduces every 13 years- Only once every 221 years do the sibling species release gametes at the same timeEx: Primates: 2-4 estrus cycles/yearHumans: Estrus all year longReproductive Isolating MechanismsPrezygotic Isolation:4. Ethological isolation: - isolated by behaviors- copulation proceeded by courtship displays - reciprocity produces sexual stimulationEx: Birds - Females genetically equipped to recognize behavioral signals by males - Females of other species are not genetically equipped to recognize these signalsReproductive Isolating MechanismsPrezygotic isolation:5. Mechanical isolation: Isolated by incompatible reproductive part size or shapeEx: Insects (Tsetse flies) Mechanical isolation is often severe, wrong mating types can result in mortality to both males and femalesMaleFemalePenisVaginaPenile appendagePenile receptacleReproductive Isolating MechanismsPrezygotic Isolation:6. Gametic isolation (incompatibility): - gametes of different species are incompatible at the molecular level resulting in mortality Ex: Plant (pollen grains) Gametic wastage: - minimum # of sperm required per species to achieve fertilizationEx: HumansReproductive Isolating MechanismsPostzygotic Isolation: Isolation takes effect after fertilization1. Zygotic Wastage:Minimum # of zygotes required per species to achieve a viable adult. Ex: fish and invertebrates2. Hybrid Sterility:


View Full Document

UCSB EEMB 2 - Lec #14 EEMB 2 SM17 1S (Genetic Divergence Reproductive Isolation)

Download Lec #14 EEMB 2 SM17 1S (Genetic Divergence Reproductive Isolation)
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Lec #14 EEMB 2 SM17 1S (Genetic Divergence Reproductive Isolation) and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lec #14 EEMB 2 SM17 1S (Genetic Divergence Reproductive Isolation) 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?