Genetic Diversity

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Genetic Diversity
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Selection for white spotting in Dutch Rabbits
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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

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Genetic Polymorphism

• Polymorphism is the maintenance of genetic
  variability within a population
• Polymorphism has been widely observed in many
  species

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Polymorphism in Grackles
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DDT resistance in mosquitoes
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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

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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

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Fitness

• evolutionary fitness is a measure of the number
  of offspring an individual produces

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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

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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 all
  individuals will be susceptible to the same
  problems

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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

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Ngorongoro Crater
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Lions at Ngorongoro Crater
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Vipera berus - adder
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Glanville Fritillary Butterfly
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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

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Austrian Ibex Capra ibex ibex
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Turkish Ibex Capra ibex aegagrus
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Nubian Ibex Capra ibex nubiana
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Optimum outbreeding in Japanese Quail