Solving a Genetic Mystery

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Gene: a region of DNA where a specific set of instructions for one trait is kept. We get some of our genes from our mother and some from our father... more

Inheritance: genetic information passed down from a parent.

Phenotype: the appearance of an individual that results from the interaction between their genetic makeup and the environment. Phenotypic trait... more

Trait: a characteristic of an organism that can be the result of genes and/or influenced by the environment. Traits can be physical like hair color or the shape and size of a plant leaf. Traits can also be behaviors such as nest building behavior in birds.

Below is a list of phenotypes easily identified in humans that follow the pattern of Mendelian inheritance. Look at yourself in the mirror to see if you carry the dominant or recessive alleles for these traits.

Mendelian Traits In Humans 

Cleft chin (dominant)      Chin without a cleft (recessive)

cleft chin


chin without cleft

Cheek dimples (dominant)

  No cheek dimples (recessive)

Cheek dimples


no cheek dimples

Free (dominant) earlobes   Attached (recessive) earlobes

unattached earlobe


attached earlobe

Face freckles (dominant)   No face freckles (recessive)

face freckles


no face freckles

No Hitchhiker's thumb (dominant)
  Hitchhiker's thumb (recessive)

hitckhiker's thumb


normal thumb

Widow's peak (dominant)   No Widow's peak (recessive)

widow's peak hairline


flat hairline

The expression of traits, however, is often far more complicated than in those listed above or those which Mendel observed in his garden. Sometimes tens, or even hundreds of genes can play a role in just one trait! In some cases, genes can block or exaggerate processes in the cell which change the visible phenotype. In other cases, environmental factors such temperature, light, and nutrient levels influence the development of a phenotype. Below is a list of traits in humans involving interaction between multiple genes.

Non-Mendelian Traits in Humans

Eye color       

black eyes


brown/black eyes

blue eyes



green eyes


Hair Color  


red hair


black hair

brown hair


blonde hair

Ability to roll tongue


rolled tongue


not rolled tongue



List of Mendelian traits in humans. In Wikipedia. Retrieved July 20, 2010, from

Additional images via Wikimedia. Close up of iris by Petr Novák.

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Bibliographic details:

  • Article: Human Traits
  • Author(s): Dr. Biology
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: July 20, 2010
  • Date accessed: September 19, 2018
  • Link:

APA Style

Dr. Biology. (2010, July 20). Human Traits. ASU - Ask A Biologist. Retrieved September 19, 2018 from

American Psychological Association. For more info, see

Chicago Manual of Style

Dr. Biology. "Human Traits". ASU - Ask A Biologist. 20 July, 2010.

MLA 2017 Style

Dr. Biology. "Human Traits". ASU - Ask A Biologist. 20 Jul 2010. ASU - Ask A Biologist, Web. 19 Sep 2018.

Modern Language Association, 7th Ed. For more info, see
Close up showing a blue colored eye with hazel flecks

Eye color is not a Mendelian trait because it is controlled by several genes, in addition to other factors.

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