Mendelian traits in humans

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Mendelian traits in humans concerns how, in Mendelian inheritance, a child receiving a dominant allele from either parent will have the dominant form of the phenotypic trait or characteristic. Only those that received the recessive allele from both parents, known as zygosity, will have 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.


These traits include:

Sickle-cell disease is inherited in the autosomal recessive pattern.

Questionable traits[edit]

May be Mendelian but there is conflicting evidence:

Traits previously believed to be Mendelian[edit]

Some traits were previously believed to be Mendelian, but their inheritance is likely based on more complex genetic models[citation needed], 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[edit]


  1. ^
  2. ^
  3. ^
  4. ^ 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
  5. ^ McDonald, J.H. 2011. Myths of Human Genetics. University of Delaware.

Further reading[edit]

External links[edit]