Editing Overdominance (section)

== Examples ==

=== Sickle cell anemia ===
An example of overdominance in humans is that of the [[sickle cell anemia]]. This condition is determined by a single [[Polymorphism (biology)|polymorphism]]. Possessors of the deleterious allele have lower life expectancy, with [[Zygosity|homozygotes]] rarely reaching 50 years of age. However, this allele also yields some resistance to [[malaria]]. Thus in regions where malaria exerts or has exerted a strong selective pressure, sickle cell anemia has been selected for its conferred partial resistance to the disease. While homozygotes will have either no protection from malaria or a dramatic propensity to sickle cell anemia, [[Zygosity|heterozygotes]] have fewer physiological effects and a partial resistance to malaria.<ref>{{Cite journal |last1=Aidoo |first1=Michael |last2=Terlouw |first2=Dianne J |last3=Kolczak |first3=Margarette S |last4=McElroy |first4=Peter D |last5=ter Kuile |first5=Feiko O |last6=Kariuki |first6=Simon |last7=Nahlen |first7=Bernard L |last8=Lal |first8=Altaf A |last9=Udhayakumar |first9=Venkatachalam |date=April 2002 |title=Protective effects of the sickle cell gene against malaria morbidity and mortality |url=https://linkinghub.elsevier.com/retrieve/pii/S0140673602082739 |journal=The Lancet |language=en |volume=359 |issue=9314 |pages=1311–1312 |doi=10.1016/S0140-6736(02)08273-9|pmid=11965279 |s2cid=37952036 |url-access=subscription }}</ref>

=== Salmonoid major histocompatibility complex ===
[[Major histocompatibility complex]] (MHC) genes exhibit extensive variation, generally attributed to the notion of heterozygous individuals identifying a wider range of peptides than homozygous individuals. In [[arctic char]] population in [[Finland]], fish heterozygous for MHC alleles had fewer cysts, grew larger, and had a better chance at survival, all indicating a higher fitness of the heterozygotes.<ref name=":0">{{Cite journal |last1=Kekäläinen |first1=Jukka |last2=Vallunen |first2=J. Albert |last3=Primmer |first3=Craig R. |last4=Rättyä |first4=Jouni |last5=Taskinen |first5=Jouni |date=2009-09-07 |title=Signals of major histocompatibility complex overdominance in a wild salmonid population |journal=Proceedings of the Royal Society B: Biological Sciences |volume=276 |issue=1670 |pages=3133–3140 |doi=10.1098/rspb.2009.0727|pmid=19515657 |pmc=2817134 }}</ref>

=== ''Gymnadenia rhellicani'' colour polymorphism ===
In ''[[Gymnadenia rhellicani]]'', flower pigmentation is controlled by changes to [[amino acid]]s 612 and 663 in GrMYB1, which plays a role in [[anthocyanin]] pigment production. Red flowers, heterozygous with black and white alleles, maintain a reproductive fitness advantage over white and black varieties presumably because they attract both bee and fly pollinator populations. Since the emergence of the white allele, the frequency of the red phenotype has been increasing in wild populations in multiple regions of the alps.<ref name=":1">{{Cite journal |last1=Kellenberger |first1=Roman T. |last2=Byers |first2=Kelsey J. R. P. |last3=De Brito Francisco |first3=Rita M. |last4=Staedler |first4=Yannick M. |last5=LaFountain |first5=Amy M. |last6=Schönenberger |first6=Jürg |last7=Schiestl |first7=Florian P. |last8=Schlüter |first8=Philipp M. |date=2019-01-08 |title=Emergence of a floral colour polymorphism by pollinator-mediated overdominance |journal=Nature Communications |language=en |volume=10 |issue=1 |pages=63 |doi=10.1038/s41467-018-07936-x |pmid=30622247 |pmc=6325131 |bibcode=2019NatCo..10...63K |issn=2041-1723}}</ref>