Population Genetics and Speciation Slide 2 1. Population
Genetics 2. Microevolution 3. Gene Pool 4. Allele Frequency 5.
Phenotype Frequency A. Total genetic information in a population B.
Portion of gene copies of a given allele C. Study of the frequency
and interaction of alleles and genes in populations D. Change in
the collective genetic material of a population E. Ratio of
individuals with a given phenotype to the total population Slide 3
A. Population GeneticsC B. MicroevolutionD C. Gene PoolA D. Allele
FrequencyB E. Phenotype FrequencyE Slide 4 Population Genetics is
the study of evolution from a genetic point of view (it is the
study of microevolution) Microevolutiona change in the collective
genetic material of a population Populationmembers of the same
species that can interbreed. It is the smallest unit in which
evolution occurs.
http://www.abc.net.au/science/news/enviro/EnviroRepublish_1417697.htm
Slide 5 Populations show natural variety within a species. Many
quantitative traits (height and weight etc.) follow a bell shaped
curve. http://www.bulbnrose.org/Heredity/Mather/poly1.jpg Slide 6
Environmental factorsamount of food, quality of food, etc. Genetic
factors Mutationsrandom changes in genes Recombinationreshuffling
of genes Random pairing of gametes Slide 7 Gene pool total genetic
information available in a population
http://www.cartoonstock.com/lowres/rde3053l.jpg Slide 8 Allele
frequencyexpressed as a percent: it is determined by dividing the
number of a certain allele by the total number of alleles of all
types in the population Phenotypic frequencyexpressed as a percent:
it is the number of individual with a particular phenotype divided
by the total number of individuals in the population. Slide 9
Developed by Wilhelm Weinberg (German physician) and Godfrey Hardy
(British mathematician)
http://anthro.palomar.edu/synthetic/synth_2.htm Godfrey
HardyWilhelm Weinberg Slide 10 States that genetic frequencies in a
population tend to remain the same from generation to generation
unless acted on by outside influences. It is based on a
hypothetical population that is not evolving.
http://www.cartoonstock.com/directory/h/human_evolution.asp Slide
11 In Genetic Equilibrium: No net mutations occur Population size
remains constant The population is infinitely large Individuals
mate randomly Selection does not occur This flock of mallards
probably violates some or all of the conditions necessary for the
Hardy-Weinberg genetic equilibrium
http://mariewinnnaturenews.blogspot.com/2007_11_25_archive.html
Slide 12 It is highly unlikely that all five of the conditions in
the Hardy-Weinberg Model will happen in the real world. Therefore,
Genetic Equilibrium is impossible in nature. It is a theoretical
state that allows us to consider what forces could disrupt such
balance (equilibrium). Slide 13 1. Immigration 2. Emigration 3.
Gene Flow 4. Genetic Drift 5. Sexual Selection 6. Stabilizing
Selection 7. Disruptive Selection 8. Directional Selection A.
Individuals move out B. Individuals move in C. Choice of mates
based on favorable traits D. Genes move from one population to
another E. Average trait is selected F. One extreme trait is
selected G. Two extreme traits are selected H. Allele frequencies
change randomly Slide 14 1. ImmigrationB 2. EmigrationA 3. Gene
FlowD 4. Genetic DriftH 5. Sexual SelectionC 6. Stabilizing
SelectionE 7. Disruptive SelectionG 8. Directional SelectionF Slide
15 Disruptions to the Hardy-Weinberg equilibrium can result in
evolution. The five requirements for genetic equilibrium can be
disrupted by the following outside forces: Mutation Gene Flow
Genetic Drift Nonrandom Mating Natural Selection Slide 16 Mutations
occur constantly at very low rates under normal conditions.
Exposure to mutagens (mutation- causing agents, i.e. radiation and
chemicals) can increase mutations rates. Mutations produce new
alleles for a trait They can be harmful, harmless or helpful
Helpful mutations are a vital part of evolution. Slide 17
Individuals enter and leave populations constantly. Their genes
move with them. This is called Gene Flow. Factors influencing gene
flow include: Immigrationmovement of individuals into a population
Emigrationmovement of individuals out of a population Migration and
dispersal patterns can also influence the movement of individuals
into new populations Birth and Death Rates also remove or add genes
from individuals to a population. Slide 18 In nature, population
sizes are restricted rather than infinitely large. Genetic Drift
can occur in small populations of organisms Genetic Driftthe random
change in allele frequency in a population Significant changes can
happen in small populations if even a single organism either fails
to reproduce or reproduces too much. Slide 19 If the frequency of
an allele reaches zero in a population, then (assuming you started
with two alleles), there is only one left. All individuals will be
homozygous for that trait---creating no variations. This weakens a
species. Ex: Northern Elephant Seal Homozygous for every gene
tested
http://en.wikipedia.org/wiki/File:Northern_Elephant_Seal,_San_Simeon2.jpg
Slide 20 Genetic Drift can lead to a bottleneck effect in which
variations are reduced overtime.
http://biology.unm.edu/ccouncil/Biology_203/Summaries/PopGen.htm
Slide 21 Organisms do not mate randomly in nature. Mate selection
is influence by: Geographic proximity choose mates nearby: can
result in kinship mating Assortative Mating choose mates with
similar traits: reduces variation Sexual Selectionchoose mates
based on favorable traits
http://upload.wikimedia.org/wikipedia/commons/5/51/Oregon_zoo_peacock_male.jpg
Slide 22 Natural Selectionorganisms with favorable traits are more
likely to survive and reproduce, passing on their favorable genes
to the next generation. It is an ongoing process in nature and an
important disruption to equilibrium. Three patterns of Natural
Selection: Slide 23 Stabilizing Selection: individuals with the
average form of a trait have the highest fitness. Ex: Lizard body
size
http://upload.wikimedia.org/wikipedia/commons/c/c6/Selection_Chart.PNG
Slide 24 Disruptive Selection: individuals with either extreme
variation of a trait have the highest fitness. Ex: Shell Color of
Limpets
http://upload.wikimedia.org/wikipedia/commons/c/c6/Selection_Chart.PNG
Slide 25 Directional Selection: individuals with one extreme of a
trait have the highest fitness Ex: Nose and tongue lengths of
anteaters
http://upload.wikimedia.org/wikipedia/commons/c/c6/Selection_Chart.PNG
Slide 26 1. Speciation 2. Geographic Isolation 3. Allopatric
Speciation 4. Reproductive Isolation 5. Sympatric Speciation 6.
Gradualism 7. Punctuated Equilibrium A. A slow change in a species
over millions of years B. Bursts of rapid change C. Formation of a
new species D. Physical separation of populations E. Inability to
mate or produce offspring F. Speciation resulting from geographic
isolation G. Speciation resulting from reproductive isolation Slide
27 1. SpeciationC 2. Geographic IsolationD 3. Allopatric
SpeciationF 4. Reproductive IsolationE 5. Sympatric SpeciationG 6.
GradualismA 7. Punctuated EquilibriumB Slide 28 Speciationformation
of a new species Species: a single kind of organism whose members
are morphologically similar and can interbreed to produce fully
fertile offspring. Two types of speciation: Allopatric Speciation
and Sympatric Speciation Slide 29 Allopatric Speciation: species
arise as a result of geographic isolation. (Allopatric = different
homelands) Geographic Isolationphysical separation of members of a
population Gene flow between the new subpopulations stops and the
two begin to diverge Eventually, they become incompatible for
mating, creating new species. Debate exists as to whether or not
allopatric species are different enough to be considered new
species. Slide 30
http://cas.bellarmine.edu/tietjen/images/geographic_isolation.jpg
http://evolution.berkeley.edu/evosite/history/images/geog_isolation.gif
Examples of Geographic Isolation Slide 31 Sympatric Speciation
occurs when two subpopulations become reproductively isolated
within the same geographic area. Reproductive Isolationthe
inability of members of the same species to mate Can be caused by
disruptive selection Two types: prezygotic isolation and
postzygotic isolation Slide 32 Prezygotic (premating) isolation:
(different mating seasons, different mating calls, etc.) Behavioral
Isolation Slide 33 Habitat Isolation Temporal Isolation Mechanical
Isolation Gametic Isolation Other Prezygotic Isolation Mechanisms
include Slide 34 Postzygotic (postmating) isolation: offspring do
not fully develop, die, or are infertile. Hybrid is weak and likely
to dieHybrid is sterile Slide 35
http://www.geo.arizona.edu/Antevs/nats104/SymptrcSpctnSml.jpg Slide
36 Two Theories: Gradualism slow change over millions of years
Punctuated Equilibriumshort bursts of rapid change
http://bioap.wikispaces.com/file/view/gradualism.gif/94608242/gradualism.gif
Slide 37 Evidence exists that suggests that both have taken place
over time.
http://silvertonconsulting.com/blog/wp-content/uploads/2010/06/c7-1-23-finches.jpg
http://www.doctortee.com/dsu/tiftickjian/cse-img/biology/evolution/horse-evolution-2.jpg
Slide 38 Hardy and Weinberg went on to develop an equation that can
be used to discover the probable genotype frequencies in a
population and to track their changes from one generation to
another. The equation is: p 2 +2pq+q 2 = 1 p= frequency of the
dominant allele q = frequency of the recessive allele See handout
Slide 39 Punnett Squares allow geneticists to predict the
probability of offspring genotypes for particular traits based on
the known genotypes of their two parents The Hardy-Weinberg
equation essentially allowed geneticists to do the same thing for
entire populations. Slide 40 Before Hardy and Weinberg, it was
thought that dominant alleles must, over time, wipe out recessive
alleles (genophagy = gene eating) According to this wrong idea,
dominant alleles always increase in frequency from generation to
generation. Hardy and Weinberg demonstrated that dominant alleles
can just as easily decrease in frequency.
