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Information for the Term Paper. Goal – about 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

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information for the term paper
Information for the Term Paper
  • Goal – about 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
use of webpages as sources
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
  • Main value of webpages is they may provide very current information – but reader beware:
  • Webpages are not archived
  • Webpages are not peer-reviewed


Evaluating Internet Research Sources

Robert Harris

Version Date: November 22, 2010Previous Version: June 15, 2007

"The central work of life is interpretation." --Proverb

measuring genetic diversity
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
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
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
genetic polymorphism
Genetic Polymorphism
  • Polymorphism is the maintenance of genetic variability within a population
  • Polymorphism has been widely observed in many species
direct observation of genetic variation
Direct Observation of Genetic Variation
  • Originally done by protein gel electrophoresis
  • DNA hybridization was another early method
  • Now mostly done by directly sequencing DNA – either in small fragments or entire genomes
extent of polymorphism
Extent of Polymorphism
  • Electrophoretic studies have generally found about 25% of all loci tested to be polymorphic - humans 28%, chimps 5%, 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 mechanisms
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
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
what do hs and dst tell us
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
  • evolutionary fitness is a measure of the number of offspring an individual produces
loss of fitness
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
reasons for loss of fitness
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
  • Inbreeding depression is the loss of fitness resulting from the breeding of closely related individuals - it occurs due to the three reasons listed before
outbreeding depression
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
  • evolutionary fitness is a measure of the number of offspring an individual produces
maintenance of polymorphism
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 polymorphism46
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
maintenance of polymorphism51
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
maintenance of polymorphism53
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:
  • selection acts to maintain stable polymorphism so that different genotypes are most fit under different situations
  • fixation of a particular genotype is counteracted by mutation
  • fixation of a particular genotype in one population is counteracted by gene flow from another population
  • 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
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
allen s rule in foxes
Allen’s Rule in Foxes

Arctic Fox Desert (Kit) Fox


Cline in



by white