Mendelian traits in humans

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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.

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.

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^[3]
• Ehlers–Danlos syndrome^[2]: 53
• Fabry disease^{[citation needed]}
• Galactosemia^[2]: 53
• Gaucher's disease^{[citation needed]}
• Haemophilia^[2]: 53
• Hereditary breast–ovarian cancer syndrome^{[citation needed]}
• Hereditary nonpolyposis colorectal cancer^{[citation needed]}
• HFE hereditary haemochromatosis
• Huntington's disease^[2]: 53
• Hypercholesterolemia^[2]: 53
• Krabbe disease^{[citation needed]}
• Lactase persistence (dominant) ^[4]
• Leber's hereditary optic neuropathy^{[citation needed]}
• Lesch–Nyhan syndrome^[2]: 53
• Marfan syndrome^[2]: 53
• Niemann–Pick disease^{[citation needed]}
• Phenylketonuria^[2]: 53
• Porphyria^[2]: 53
• Retinoblastoma^{[citation needed]}
• Sickle-cell disease^[2]: 53
• Sanfilippo syndrome^{[citation needed]}
• Tay–Sachs disease^[2]: 53
• Wet (dominant) or dry (recessive) earwax – dry is found mostly in Asians and Native Americans^[5]

References[]

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).
• 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. S2CID 89318627. Lay summary (4 September 2010).

External links[]

• OMIM Online Mendelian Inheritance in Man
• Myths of Human Genetics