Quantitative Traits

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Quantitative Traits

• Multigenic phenotypes
• Chapter 8.1, 8.3, 8.5, 8.6, 8.7

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• Qualitative Traits
• Typical mendelian traits
• No overlap between classes of phenotypes
• Tall pea plants
• Short pea plants
• Single genes

• Quantitative traits
• Blending
• Overlap, no discreet classes
• Height in Humans
• Swimmng Speed
• Multigenic interactions
• Overlapping of Environmental and genic
  interactions

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Quantitative Traits and Mendel

• Mendelian genetics explains quantitative traits,
  if one assumes multiple genes and some incomplete
  dominance

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Measuring Heritable Variation

• Differences in Phenotypes in quantitative trait
• Environment
• Genetics
• Heritability
• Fraction of total phenotypic variation (VP)
  within a population that is due to genetic
  differences (VG)

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Narrow-Sense heritability

• Total Genetic variance is the sum of additive
  gene interaction (VA), Dominance interactions
  (VD), and other interactions
• Narrow-sense heritability (h2) is only concerned
  with VA

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• h2 can be measured as slope of a line of a plot
  of offspring values vs. parental values
• Why do we concern ourselves with h2?
• selection

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H2 and Selection

• Additive gene interactions respond quickly to
  selection
• Heritabilty studies can help you understand
  evolutionary history and response

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What heritability cant tell you

• Heritabilities are snap shots in time
• Depending on environment traits can exhibit
  higher or lower values
• Heritabilities do not predict mean values for
  phenotype between populations, nor how those
  genotypes will react in differenct environments

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• Achilla is a native wildflower
• Height in Achilla is highly heritable
• Identical clippings grown it Mather and Stanford
  experimental gardens
• Another trait in Achilla is number of stems
• Low Altitude plants make more stems than high
  altitude plants

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Experiment Culture low and high altitude plants
to new altitudes
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Bell Curve fallacy
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Experiment to test Bell Curve Hypothesis
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• Heritability does not mean genetic
• Heritability is not a permanent feature
• Heritability only predicts what will happen to a
  population under specific conditions

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End of Chapter problems

• Chapt. 8 4, 5, 6, 7
• Chapt. 7 1, 2
• Chapt. 6 6, 7, 8, 9, 10, 11, 16