Falconer's formula

Falconer's formula is a mathematical formula that is used used in twin studies to estimate the relative contribution of genetics vs. environment to variation in a particular trait (that is, the heritability of the trait) based on the difference between twin correlations.[1] It was first proposed by the Scottish geneticist Douglas Falconer.[2]

The formula is

Hb2 = 2(rmz - rdz)

where Hb2 is the broad sense heritability, rmz is the (monozygotic, MZ) identical twin correlation, and rdz is the (dizygotic, DZ) fraternal twin correlation. The correlation of same sex MZ twins is always higher than the DZ twin correlation with various sexes and thus all gender differences are evaluated as heritable. To avoid this error, only genetic studies comparing MZ twins with the same sex DZ twins are valid. Correlations between A = hb2 (additive genetics) and C (common environment) must be included in the derivation shown below.

rmz = A + C + 2 Corr(A,C)
rdz = ½A + C + 2 Corr(½A,C)

Falconer's formula is based on assumptions that have been widely criticized as flawed. For example, it only calculates narrow-sense heritability, meaning it assumes that all genetic effects are additive; this assumption does not comport with the functioning of genes in real biological systems.[3] The formula also overestimates broad-sense heritability due to an overestimation of dominance variance.[4]

See also

References

  1. ↑ Weber WW (2008). "Chapter 5: Genetics in Pharmacology: Twin Studies". Pharmacogenetics (2nd ed.). Oxford: Oxford University Press. pp. 107–8. ISBN 978-0-19-971216-8.
  2. ↑ Falconer DS, Mackay TF (1998). Introduction to quantitative genetics (4th ed.). Essex: Longman Group, Ltd. ISBN 978-0-582-24302-6.
  3. ↑ Gordon H, Trier Moller F, Andersen V, Harbord M (June 2015). "Heritability in inflammatory bowel disease: from the first twin study to genome-wide association studies". Inflammatory Bowel Diseases. 21 (6): 1428–34. doi:10.1097/mib.0000000000000393. PMC 4450891. PMID 25895112.
  4. ↑ Weber W (2008-04-02). Pharmacogenetics. Oxford Monographs on Medical Genetics. 55 (2nd ed.). Oxford University Press. pp. 107–108. ISBN 978-0-19-971216-8.


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