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Information for the Term Paper
• Goal – at least 10 pages long, will need at least 10
references
• Use the primary literature for your references – reports of
original research and ideas
• Primary literature is usually published as research or
review papers in scholarly journals, or in scientific books
• Example journals – Science, Nature, Conservation
Biology, Environmental Management, Ecology, Applied
Ecology, Annual Review of Ecology and Systematics, etc.
• Do not use secondary literature – general works based on
primary literature – popular books and magazines –
Discover, Natural History, National Geographic, Scientific
American, Smithsonian, etc.
Use of Webpages as Sources
• You may need to use webpages for most
up-to-date material but:
• No more than 3 webpages for paper; or if
more than 10 references – no more than
30% from webpages
• Main value of webpages is they may
provide very current information – but
reader beware:
• Webpages are not archived
• Webpages are not peer-reviewed
:VirtualSalt
Evaluating Internet Research Sources
Robert Harris
Version Date: December 27, 2013
Previous Version: June 15, 2007
"The central work of life is interpretation." --Proverb
http://www.virtualsalt.com/evalu8it.htm
Genetic Diversity
What is Genetic Diversity?
• Genetic diversity is the diversity that occurs in
genes of individuals and species
• Genetic diversity originates with mutations
• It is probably best to think of genetic diversity as
occurring at 4 different levels:
1. among species
2. among populations
3. within populations
4. within individuals
Measuring Genetic Diversity
• Among and within populations we often measure genetic
diversity by measuring polymorphism - the percentage of
genes that are polymorphic (have several alleles) within a
population
• Polymorphism is sometimes also considered to be a
process - the maintenance of genetic diversity within a
population
• We can also measure genetic diversity by measuring
heterozygosity - the percentage of genes at which the
average individual is heterozygous
Importance of Genetic Diversity
• Beginning with Darwin, most evolutionary
biologists have thought that rather small
heritable changes provide most of the
variation on which natural selection acts
• These small changes are most obvious when
using measurable characters such as size or
yield - typically they result in continuous
variation seen when graphing size as a bell
curve
Continuous variation:
Selection for
white spotting
in Dutch Rabbits
Cause of Continuous Variation
• The genetic cause for these changes are
genes with small phenotypic effect called
multiple factors or polygenes –
• Polygenes are where several genes interact
to produce a quantitative phenotypic effect
on a character
Mutation is the source of
genetic variation
Common mutation – black color
in grey squirrels
Mutation Rates
Genetic Polymorphism
• Polymorphism is the maintenance of genetic
variability within a population
• Polymorphism has been widely observed in
many species
Polymorphism in Grackles
Direct Observation of Genetic
Variation
• Originally done by protein gel
electrophoresis – still commonly used
• DNA hybridization was another early
method
• Now mostly done by directly sequencing
DNA – either in small fragments or entire
genomes
Protein Gel Electrophoresis
Hominid relationships – based on
gel electrophoresis
DNA Hybridization
Hominid relationships – based on
DNA hybridization
DNA Sequencing
Hominid relationships – based on
mitochondrial DNA sequencing
Extent of Polymorphism
• Electrophoretic studies have generally found about 25% of
all loci tested to be polymorphic - humans - 28%,
drosophila - 43%
• It is generally thought that only one-third of genetic
differences are detected by electrophoresis – this is due to
the presence of silent substitutions – for example: GGU,
GGC, GGA, and GGG all code for Glycine
• Thus it is possible that two-thirds to three-fourths of all
loci are polymorphic in a species and that an average
individual is heterozygous at about 25% of its loci
DDT resistance in mosquitoes
DDT Resistance Mechanisms
• an increase in lipid content that lets fat-soluble
DDT separate from other parts of the organism
• presence of enzymes that break down DDT into
relatively less toxic products
• reduced toxic response of the nervous system to
DDT
• differences in permeability of insect cuticle to
DDT absorption
• behavioral response that limits contact with DDT
Comparing Heterozygosity
• When comparing heterozygosity of different
species we usually look at total genetic diversity symbolized Ht
• Ht is composed of two aspects of heterozygosity –
• Hs - genetic diversity within the populations that
compose the species
• and Dst - genetic diversity due to variability
among the populations
• thus Ht = Hs + Dst
Some heterozygosity
What do Hs and Dst tell us?
• Species with widely scattered populations
that don’t exchange genes (like desert pup
fish in ponds in Death Valley) tend to have
very high Dst
• Species with populations that do exchange a
lot of genes (like pines) tend to have high
Hs – Humans also have high Hs
Fitness
• evolutionary fitness is a measure of the
number of offspring an individual produces
Loss of Fitness
• Another important aspect of polymorphism
is that it tends to maintain fitness • populations of animals in zoos, which are
typically low in genetic diversity, often
have low fitness - low fertility and high
mortality among offspring
Fitness of Zoo Animals
Reasons for Loss of Fitness
1. increased incidence of deleterious recessive
homozygous individuals
2. lack of heterosis – heterosis (hybrid vigor) is the
phenomenon where heterozygous individuals have
higher fitness than do homozygotes - often
heterozygotes are more resistant to disease
3. lack of evolutionary potential - with all
homozygotes there is lack of variation and thus
limited ability to respond to environmental
changes
Inbreeding Depression
• Inbreeding depression is the loss of fitness
resulting from the breeding of closely
related individuals - it occurs due to the
three reasons listed before
Ngorongoro Crater
Lions at Ngorongoro Crater
Vipera berus - adder
Glanville Fritillary Butterfly
Outbreeding Depression
• The loss of fitness that occurs when
distantly related individuals breed –
• This occurs because certain populations
may have been selected for traits that are
successful in their environment, so that
introducing novel traits may reduce fitness
for that environment
Austrian Ibex – Capra ibex ibex
Turkish Ibex – Capra ibex aegagrus
Nubian Ibex – Capra ibex nubiana
Optimum outbreeding in
Japanese Quail
Fitness
• evolutionary fitness is a measure of the
number of offspring an individual produces
Maintenance of Polymorphism
without natural selection • random mating tends to
maintain polymorphism –
due to the benefits of
sexual reproduction –
recombination,
independent assortment,
and crossing over
Maintenance of Polymorphism
• The effects of nonrandom mating are
variable - species may either mate
assortatively (like with like) or
disassortatively (like with unlike)
• assortative mating results in many
homozygous individuals
• disassortative with many polymorphic,
heterozygous individuals
Assortative Mating - Three spined
stickleback
Disassortative Mating –
Nonbreeding Ruff
Disassortative Mating - Breeding male
ruff and variations on head pattern
Maintenance of Polymorphism
• environmental variance - the environment
may affect development of different
genotypes so that which genotype
dominates changes with the environment if the environment varies or different
habitats exist within the species range, then
different genotypes will exist
Backswimmers – winged or
wingless forms
Maintenance of Polymorphism
With Natural Selection
• with selection, we would expect the most fit
genotype to come to dominate the population, but
polymorphism may still occur:
1. selection acts to maintain stable polymorphism
so that different genotypes are most fit under
different situations
2. fixation of a particular genotype is counteracted
by mutation
3. fixation of a particular genotype in one
population is counteracted by gene flow from
another population
Polymorphism under selection –
in the Grove Snail - Cepaea
Clines
• in many species, local populations have
little variation, but the entire species
exhibits much variation as local populations
are adapted to different conditions - if these
changes in genes change in response to
certain environmental variables, we may see
a cline - a gradual change along a
geographic transect
Clines with Body Size
• Bergmann's rule - many animals get larger
in size as the species range approaches the
poles - it is related to ability to keep warm larger bodies maintain warmth better
• Allen’s Rule – size of extremities decreases
towards the poles – heat is lost through
things like large ears, long limbs
Bergman’s Rule in same aged
White-tailed Deer
Allen’s Rule in Foxes
Arctic Fox
Desert (Kit) Fox
Allen’s Rule in Hares
Cline in Cyanide Production in
White Clover
Cline in
cyanide
production
by white
clover
Greater Racquet-tailed Drongo
cline in crest size