Simple Mendelian genetics in humans

Mendelian traits behave according to the model of monogenic or simple gene inheritance in which one gene corresponds to one trait. Discrete traits (as opposed to continuously varying traits such as height) with simple Mendelian inheritance patterns are relatively rare in nature, and many of the clearest examples in humans cause disorders. Discrete traits found in humans are common examples for teaching genetics.

Mendelian model

According to the model of Mendelian inheritance, alleles may be dominant or recessive, one allele is inherited from each parent, and only those who inherit a recessive allele from each parent exhibit the recessive phenotype. Offspring with either one or two copies of the dominant allele will display the dominant phenotype.

Very few phenotypes are purely Mendelian traits. Common violations of the Mendelian model include incomplete dominance, codominance, genetic linkage, environmental effects, and quantitative contributions from a number of genes (see: gene interactions, polygenic inheritance, oligogenic inheritance).^[1][2]

OMIM (Online Mendelian Inheritance in Man)^[3] is a comprehensive database of human genotype–phenotype links. Many visible human traits that exhibit high heritability were included in the older McKusick's Mendelian Inheritance in Man. Before the discovery of genotyping, they were used as genetic markers in medicolegal practice, including in cases of disputed paternity.

Human traits with probable or uncertain simple inheritance patterns

Dominant	Recessive	References
Low heart rate	High heart rate	[4]
Widow's peak	Straight hair line	[5][6]
Facial dimples	No facial dimples	[7][8]
Ability to taste PTC, "Taster"	Unable to taste PTC, "Nontaster"	[9]
Unattached (free) earlobe	Attached earlobe	[7][10][11]
Clockwise hair direction (left to right)	Counter-Clockwise hair direction (right to left)	[12]
Cleft chin	Smooth chin	[13]
Freckles	No freckles	[7][14]
Wet-type earwax	Dry-type earwax	[10][15]
Roman nose	No prominent bridge	[16]
Marfan syndrome	Average body proportions and connective tissue	[17]
Huntington's disease	No nerve damage	[18]
Normal mucous lining	Cystic fibrosis	[19]
Photic sneeze reflex	No light-induced sneeze reflex	[20]
Forged chin	Receding chin	[16]
White forelock present	No white forelock	[21]
Ligamentous angustus	Ligamentous Laxity	[22]
Ability to eat sugar	Galactosemia	[23]
Total leukonychia and Bart pumphrey syndrome	Partial leukonychia	[24]
Absence of fish-like body odour	Trimethylaminuria	[25]
Primary hyperhidrosis	Little sweating in hands	[26]
Lactase persistence	Lactose intolerance	[27]
Prominent chin (V-shaped)	Less prominent chin (U-shaped)	[28]
Acne prone	Clear complexion	[29]

See also

• Polygenic inheritance
• Trait
• Gene interaction
• Dominance
• Homozygote
• Heterozygote

References

1. Dobzhansky T. (1970): Mankind evolving: The evolution of the human species. Bantam Books, New York, ISBN 05526-539-0X; ISBN 978-05526-5390-9.
2. Hadžiselimović R. (2005): Bioanthropology - Biodiversity of recent man. Institute for Genetic Engineering and Biotechnology (INGEB), Sarajevo, ISBN 9958-9344-2-6. (in Bosnian).
3. OMIM-http://www.omim.org/
4. Benson, D. Woodrow; Wang, Dao W.; Dyment, Macaira; Knilans, Timothy K.; Fish, Frank A.; Strieper, Margaret J.; Rhodes, Thomas H.; George, Alfred L. (2003). "Congenital sick sinus syndrome caused by recessive mutations in the cardiac sodium channel gene (SCN5A)". Journal of Clinical Investigation. 112 (7): 1019–1028. doi:10.1172/JCI18062. PMC 198523. PMID 14523039.
5. Campbell, Neil; Reece, Jane (2005). Biology. San Francisco: Benjamin Cummings. p. 265. ISBN 0-07-366175-9.
6. McKusick, Victor A. (10 February 2009). "Widow's Peak". Online Mendelian Inheritance in Man. Johns Hopkins University. 194000.
7. "Genetics/Reproduction". ScienceNet - Life Science. Singapore Science Centre. Archived from the original on 2003-09-25.
8. McKusick, Victor A. (25 June 1994). "Dimples, Facial". Online Mendelian Inheritance in Man. Johns Hopkins University. 126100.
9. Wooding, Stephen (28 June 2004). "Natural selection at work in genetic variation to taste". Medical News Today. Archived from the original on 2007-12-13.
10. Cruz-Gonzalez, L.; Lisker, R. (1982). "Inheritance of ear wax types, ear lobe attachment and tongue rolling ability". Acta Anthropogenet. 6 (4): 247–54. PMID 7187238.
11. McKusick, Victor A.; Lopez, A (30 July 2010). "Earlobe Attachment, Attached vs. Unattached". Online Mendelian Inheritance in Man. Johns Hopkins University. 128900.
12. McDonald, John H. (8 December 2011). "Hair Whorl". Myths of Human Genetics. University of Delaware.
13. McKusick, Victor A. (23 March 2013). "Cleft Chin". Online Mendelian Inheritance in Man. Johns Hopkins University. 119000.
14. Xue-Jun Zhang; et al. (2004). "A Gene for Freckles Maps to Chromosome 4q32–q34". Journal of Investigative Dermatology. 122 (2): 286–290. doi:10.1046/j.0022-202x.2004.22244.x. PMID 15009706.
15. McKusick, Victor A.; O'Neill, Marla J. F. (22 November 2010). "Apocrine Gland Secretion, Variation in". Online Mendelian Inheritance in Man. Johns Hopkins University. 117800.
16. "Mendelian Traits in Humans" (PDF). Human Genetics. San Diego Supercomputer Center (SDSC).
17. Chen, Harold (2019-11-10). Buehler, Bruce (ed.). "Genetics of Marfan Syndrome". Medscape. WebMD LLC.
18. Stafford, Kate; Mannor, Michael. "Mutations and Genetic Disease". Genetic Diseases. ThinkQuest. Archived from the original on 2007-01-03.
19. "Autosomal Recessive: Cystic Fibrosis, Sickle Cell Anemia, Tay Sachs Disease". Medical Genetics. Children's Hospital of Pittsburgh. 3 February 2008. Archived from the original on 2009-08-24.
20. Schrock, Karen (10 January 2008). "Looking at the Sun Can Trigger a Sneeze". Scientific American. Archived from the original on 2011-03-19.
21. "Inherited Human Traits". EdQuest. Archived from the original on 2012-02-01.
22. Scott, C. I. (1971). "Unusual facies, joint hypermobility, genital anomaly and short stature: A new dysmorphic syndrome". Birth Defects Original Article Series. 7 (6): 240–246. PMID 5173168.
23. Fankhauser, D. B. (2 Feb 2006). "Human Heritable Traits". University of Cincinnati Clermont College. Archived from the original on 2012-02-23.
24. Tüzün, Yalçın; Karaku, Özge (2009). "Leukonychia" (PDF). Journal of the Turkish Academy of Dermatology. JTAD. Archived from the original (PDF) on 2016-03-03. Retrieved 2015-02-23.
25. "Learning About Trimethylaminuria". genome.gov. National Human Genome Research Institute.
26. Kaufmann, Horacio; Saadia, Daniela; Polin, Charlene; et al. (10 January 2003). "Primary hyperhidrosis - Evidence for autosomal dominant inheritance" (PDF). Clinical Autonomic Research. 13 (2): 96–98. doi:10.1007/s10286-003-0082-x. PMID 12720093. S2CID 37824317.
27. Bowen, R. (25 April 2009). "Lactose Intolerance (Lactase Non-Persistence)". Colorado State University.
28. Jablecki, Donna Mae. "Variations on a Human Face" (PDF). Science Experiments on File. Facts on File.
29. Strickland, Barbara. "Acne is a Four Letter Word". Sage Advice. Barbara Strickland. Archived from the original on 2006-02-07.

External links

• OMIM Online Mendelian Inheritance in Man
• INTERSNP - a software for genome-wide interaction analysis (GWIA) of case-control and case-only SNP data, including analysis of quantitative traits.]
• GeneticInteractions.org