List of Mendelian traits in humans
In Mendelian inheritance, a child receiving a dominant allele from either parent will have the dominant form of the trait. Only those that received the recessive allele from both parents present with the recessive phenotype. Those that receive a dominant allele from one parent and a recessive allele from the other parent will have the dominant form of the trait. Purely Mendelian traits are a tiny minority of all traits, since most phenotypic traits exhibit incomplete dominance, codominance, and contributions from many genes.
The recessive phenotype may theoretically skip any number of generations, lying dormant in heterozygous "carrier" individuals until they have children with someone who also has the recessive allele and both pass it on to their child.
Examples
These traits include:
- Wet (dominant) or dry (recessive) earwax - dry is found mostly in Asians and Native Americans[1]
- Albinism (recessive)
- Brachydactyly (shortness of fingers and toes)
- Lactase persistence (dominant)
Questionable traits
May be Mendelian but there is conflicting evidence:
- Ability to smell (bitter almond-like) hydrogen cyanide (recessive) [2]
Traits previously believed to be Mendelian
Some traits were previously believed to be Mendelian, but their inheritance is likely based on more complex genetic models, possibly involving more than one gene. These include:[3]
- Eye color
- Hair color
- Morton's toe
- Tongue rolling
- Ability to taste phenylthiocarbamide (dominant) - largely determined by a single gene, TAS2R38, with two common alleles, though there are 8 possible haplotypes[4] Because it is not a trait where the dominant tastes and the recessive cannot, but rather a continuous gradient in ability to detect PTC, it is not a real example of a simple mendelian trait. This is best exemplified by the fact that two non-tasters (recessive trait) can, in fact, have a child that can taste PTC (dominant trait). [5]
- Widow's peak (allele)
- Detached (dominant) or attached (recessive) earlobes
- Hitchhiker's thumb (recessive)
See also
References
- ↑ http://udel.edu/~mcdonald/mythearwax.html
- ↑ http://omim.org/entry/304300?search=smell%20hydrogen%20cyanide&highlight=cyanide%20smell%20hydrogen
- ↑ http://udel.edu/~mcdonald/mythintro.html
- ↑ Kim, U. K., E. Jorgenson, H. Coon, M. Leppert, N. Risch, and D. Drayna. 2003. Positional cloning of the human quantitative trait locus underlying taste sensitivity to phenylthiocarbamide. Science 299: 1221-1225
- ↑ McDonald, J.H. 2011. Myths of Human Genetics. University of Delaware. http://udel.edu/~mcdonald/mythptc.html
Further reading
- Mange, Elaine J.; Mange, Arthur R. (1999). Basic Human Genetics (second ed.). Sunderland (MA): Sinauer. ISBN 0-87893-497-9. Lay summary (16 October 2010).
- Speicher, Michael R.; Antonarakis, Stylianos E.; Motulsky, Arno G., eds. (2010). Vogel and Motulsky's Human Genetics: Problems and Approaches. Heidelberg: Springer Scientific. doi:10.1007/978-3-540-37654-5. ISBN 978-3-540-37653-8. Lay summary (4 September 2010).