Linkage

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Two exceptions to Mendelian inheritance

• Linkage genes occurring close together on a
  chromosome and not assorting independently
  (illustrated by diagram at right)
• Uniparental inheritance -genes inherited through
  mitochondria or chloroplasts

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• Incomplete dominance the heterozygous condition
  is intermediate between homozygous dominant and
  homozygous recessive

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Polygenic inheritance

• Some traits are the result of interactions
  between many genes
• Also referred to as quantitative traits
• The trait has continuous variation, rather than
  discrete categories

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Multiple alleles

• Multiple alleles for a particular gene
• Over 20 alleles for resistance to bacterial
  pathogen in Arabidopsis

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Codominance

• Both homozygotes show different traits, and the
  heterozygote shows both traits, not blended
  together
• Example?

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Epistasis

• One gene interferes with or masks the effect of
  another
• Example?

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Pleiotropy

• A single gene can produce more than one trait.

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