Mendelian traits in humans

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.

Autosomal dominant

A 50/50 chance of inheritance.

Sickle-cell disease is inherited in the autosomal recessive pattern. When both parents have sickle-cell trait (carrier), a child has a 25% chance of sickle-cell disease (red icon), 25% do not carry any sickle-cell alleles (blue icon), and 50% have the heterozygous (carrier) condition.[1]

If one parent has sickle-cell anaemia and the other has sickle-cell trait, then the child has a 50% chance of having sickle-cell disease and a 50% chance of having sickle-cell trait.[1]

An example of the codominant inheritance of some of the four blood groups.

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:

• Albinism (recessive)[2]^:53
• Achondroplasia[2]^:53
• Alkaptonuria[2]^{:53, 263}
• Ataxia telangiectasia[2]^:53
• Brachydactyly (shortness of fingers and toes)[2]^:53
• Colour blindness[2]^:53 (monochromatism, dichromatism, anomalous trichromatism, tritanopia, deuteranopia, protanopia)
• Cystic fibrosis[2]^:53
• Duchenne muscular dystrophy[2]^:53
• Ectrodactyly
• Ehlers–Danlos syndrome[2]^:53
• Fabry disease
• Galactosemia[2]^:53
• Gaucher's disease
• Haemophilia[2]^:53
• Hereditary breast–ovarian cancer syndrome
• Hereditary nonpolyposis colorectal cancer
• HFE hereditary haemochromatosis
• Huntington's disease[2]^:53
• Hypercholesterolemia[2]^:53
• Krabbe disease
• Lactase persistence (dominant)
• Leber's hereditary optic neuropathy
• Lesch–Nyhan syndrome[2]^:53
• Marfan syndrome[2]^:53
• Niemann–Pick disease
• Phenylketonuria[2]^:53
• Porphyria[2]^:53
• Retinoblastoma
• Sickle-cell disease[2]^:53
• Sanfilippo syndrome
• Tay–Sachs disease[2]^:53
• Wet (dominant) or dry (recessive) earwax – dry is found mostly in Asians and Native Americans[3]

References

1. "Inheritance of Sickle Cell Anaemia – Sickle Cell Society". Archived from the original on 2018-03-27. Retrieved 2015-12-29.
2. Klug, William S.; Cummings, Michael R.; Spencer, Charlotte A.; Palladino, Michael A. (2012). Essentials of Genetics. Pearson. ISBN 978-0-321-80311-5.
3. "Myths of Human Genetics: Earwax".

Further reading

• Mange, Elaine J.; Mange, Arthur R. (1999). Basic Human Genetics (second ed.). Sunderland (MA): Sinauer. ISBN 978-0-87893-497-3. Lay summary (16 October 2010).CS1 maint: ref=harv (link)
• 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).CS1 maint: ref=harv (link)

External links

• OMIM Online Mendelian Inheritance in Man