Quantitative Genetics

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Chapter 6-

• Quantitative Genetics

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Where were going

• Define the term
• Be able to determine the of genes involved
• Phenotype-Genotype relationships- nature vs
  nurture, particularly as it deals with
• Heritability- and as an aside, variance.

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Key points

• We can estimate the effects of multiple genes by
  making some assumptions
• 1) there are multiple genes affecting the trait.
• 2) some alleles at these sites are additive,
  while others are non-additive. Additive is just
  as in normal usage- e.g., additive alleles would
  add to your height. Non-additive would produce,
  say, all or none effects- such as plant height in
  peas- tall and short.
• 3) the genes contribute approximately equally

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¼2 1/16
¼3 1/64
¼4 1/256
¼5 1/1024
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So, lets do a few problems..
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Heritability

• This is a measure of the relative influence of
  genotype and environment on variance.
• Variance- study on your own- its basically a
  statistical measure of, well, variance. We take
  the average, the difference between the average
  and each value, and we square it we then divide
  by the of samples -1.
• What heritability means high value- lots of
  variation in population? selection will work.
• Low heritability little genetic variation
  selection wont help.

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• Broad and narrow-sense heritability- p. 121 H2
  Vg/Vp if the is close to 1, then the effect
  of environment is negligible if the is close
  to 0, the effect of the environment is large.
  You book has a situation that allows this to be
  calculated.

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• Narrow sense h2 VA/VP here we only look at
  variation in traits are additive in nature- we
  exclude dominant variance, since these traits are
  less affected by selection- if the dominant trait
  is there, it, well, dominates. The h2 is useful
  in determining how easily selection can work.
• experimental determination h2 R/S

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• Concordance if both of a pair- brothers, or
  twins, have a trait, it is concordant. Useful in
  the nature/nurture controversy.
• One of the more interesting statistics-
  Concordance homosexuality for identical twins is
  38.
• QTLs Through complicated patterns of breeding,
  and knowing where certain regions are on the
  chromosome, we can locate genes that affect
  Q.T.s.

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• http//www.narth.com/docs/whitehead2.html
• J. Michael Bailey, Michael P. Dunne, and Nicholas
  G. Martin, "Genetic and Environmental Influences
  on Sexual Orientation and Its Correlates in an
  Australian Twin Sample," J. Personal Social
  Psychology 78 (2000) 524-536.