UCSB EEMB 2 - Lec #14 EEMB 2 SM17 1S (Genetic Divergence Reproductive Isolation) (16 pages)

Previewing pages 1, 2, 3, 4, 5 of 16 page document View the full content.
View Full Document

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



Previewing pages 1, 2, 3, 4, 5 of actual document.

View the full content.
View Full Document
View Full Document

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

60 views


Pages:
16
School:
University of California, Santa Barbara
Course:
Eemb 2 - Introductory Biology III
Unformatted text preview:

Genetic Divergence The Evolutionary process Variation Natural Selection 1 Variation 2 Natural Selection 3 Genetic Divergence 4 Reproductive Isolation 5 Speciation Genetic Divergence Reproductive isolation Speciation Genetic Divergence Gene Flow The physical movement of alleles into out of a population through immigration and emigration 1 alleles are lost from a population via emigration 2 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 population Ex human populations blue jays Genetic Divergence Genetic 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 deviations from expected results because Real populations are finite in size small sample size Genetic drift tends to reduce genetic variation and leads to the homozygous condition Genetic Divergence Genetic drift 2 situations that increase the impact of genetic drift on a population rapidly alter allelic frequencies The bottleneck effect A severe reduction in population size brought about by intense selection pressure or natural disaster Ex contagious disease habitat loss hunting volcanoes etc Disruptive selection Original population New population Genetic Divergence The Bottleneck Effect 1 Survivors gene pool may no longer represent the original population 2 By chance certain alleles may be over represented under represented or eliminated 3 Genetic drift may continue to alter the gene pool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 small Ex Elephant seals severe hunting resulted in bottleneck a reduction in variation Ex Cheetah monomorphic for many genes Genetic Divergence The 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 population Original population New population Migration In the absence of gene flow natural selection will alter allele frequencies in different ways due to genetic drift Ex Isolated islands Genetic Divergence Genetic divergence Any structural functional or behavioral difference that favors reproductive isolation is a by product of genetic change 1 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 population Western Meadowlark Eastern Meadowlark Parent species barrier Time Daughter species Genetic divergence leads to differences between gene pools of the separate populations mutation natural selection genetic drift Reproductive Isolating Mechanisms The Evolutionary process Variation Natural Selection 1 Variation 2 Natural Selection 3 Genetic Divergence 4 Reproductive Isolation 5 Speciation Genetic Divergence Reproductive isolation Speciation Reproductive Isolating Mechanisms Reproductive 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 environments Types 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 Mechanisms Prezygotic Isolation 1 Ecological isolation Isolation due to adaptation to different microclimates in the same habitat Ex California Oaks Santa Ynez Valley 3 species 1 valley oak Quercus lobata 2 live oak Quercus agrifolia 3 shrub oak Quercus dumosa Quercus lobata Quercus agrifolia Quercus dumosa Separation is based on physiological mechanisms to promote conservation of water Reproductive Isolating Mechanisms Prezygotic Isolation 2 Geographic isolation Isolated by distance or geographic barriers Do not come in contact distance or barrier relative to the size of the organism Ex Louse lice 2 subspecies 1 head lice Pediculus humanus var capitis 2 body lice Pediculus humanus var vestimenti Geographic isolation is the hairless region of the neck Reproductive Isolating Mechanisms Prezygotic 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 time Ex Primates 2 4 estrus cycles year Humans Estrus all year long Reproductive Isolating Mechanisms Prezygotic Isolation 4 Ethological isolation isolated by behaviors copulation proceeded by courtship displays reciprocity produces sexual stimulation Ex Birds Females genetically equipped to recognize behavioral signals by males Females of other species are not genetically equipped to recognize these signals Reproductive Isolating Mechanisms Prezygotic isolation 5 Mechanical isolation Isolated by incompatible reproductive part size or shape Ex Insects Tsetse flies Penile Penile Vagina Penis appendage receptacle Male Female Mechanical isolation is often severe wrong mating types can result in mortality to both males and females Reproductive Isolating Mechanisms Prezygotic 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 fertilization Ex Humans Reproductive Isolating Mechanisms Postzygotic Isolation Isolation takes effect after fertilization 1 Zygotic Wastage Minimum of zygotes required per species to achieve a viable adult Ex fish and invertebrates 2 Hybrid Sterility No viable sperm or egg Ex male mule 3 Hybrid Inviability egg of one species is fertilized by sperm from another species but fertilized egg


View Full Document

Access the best Study Guides, Lecture Notes and Practice Exams

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) 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?