Editing Allele (section)

==Alleles that lead to dominant or recessive phenotypes==
{{main|Dominance (genetics)}}
In many cases, genotypic interactions between the two alleles at a locus can be described as [[Dominance (genetics)|dominant]] or [[recessive]], according to which of the two homozygous phenotypes the [[heterozygote]] most resembles. Where the heterozygote is indistinguishable from one of the homozygotes, the allele expressed is the one that leads to the "dominant" phenotype,<ref name="Essential genetics: A genomics perspective"/><ref name="pmid 28696921">{{cite journal|date=September 2017|title=ASPsiRNA: A Resource of ASP-siRNAs Having Therapeutic Potential for Human Genetic Disorders and Algorithm for Prediction of Their Inhibitory Efficacy|journal=G3|volume=7|issue=9|pages=2931–2943|doi=10.1534/g3.117.044024|pmid=28696921|doi-access=free |last1=Monga |first1=Isha |last2=Qureshi |first2=Abid |last3=Thakur |first3=Nishant |last4=Gupta |first4=Amit Kumar |last5=Kumar |first5=Manoj |pmc=5592921 }}</ref> and the other allele is said to be "recessive". The degree and pattern of dominance varies among loci. This type of interaction was first formally-described by [[Gregor Mendel]]. However, many traits defy this simple categorization and the phenotypes are modelled by [[co-dominance]] and [[Quantitative trait locus|polygenic inheritance]].<ref>{{Cite web|url=https://www.genome.gov/genetics-glossary/Allele|title=Allele|website=Genome.gov|access-date=3 July 2021|archive-date=28 June 2021|archive-url=https://web.archive.org/web/20210628215931/https://www.genome.gov/genetics-glossary/Allele|url-status=live}}</ref>

The term "[[wild type]]" allele is sometimes used to describe an allele that is thought to contribute to the typical phenotypic character as seen in "wild" populations of organisms, such as fruit flies (''[[Drosophila melanogaster]]''). Such a "wild type" allele was historically regarded as leading to a dominant (overpowering – always expressed), common, and normal phenotype, in contrast to "[[mutant]]" alleles that lead to recessive, rare, and frequently deleterious phenotypes. It was formerly thought that most individuals were homozygous for the "wild type" allele at most gene loci, and that any alternative "mutant" allele was found in homozygous form in a small minority of "affected" individuals, often as [[genetic diseases]], and more frequently in heterozygous form in "[[Genetic carrier|carriers]]" for the mutant allele. It is now appreciated that most or all gene loci are highly polymorphic, with multiple alleles, whose frequencies vary from population to population, and that a great deal of genetic variation is hidden in the form of alleles that do not produce obvious phenotypic differences. Wild type alleles are often denoted by a superscript plus sign (''i.e.'', ''p{{sup|+}}'' for an allele ''p'').<ref>{{cite book|title = Genetics A Conceptual Approach|edition = 7|author = B. A. Pierce|publisher = Macmillan|date = 2020|isbn = 978-1-319-21680-1|page = 60}}</ref>