Ma'anar ƙamus na kalmar "allele" ɗaya ne daga cikin nau'i biyu ko fiye na madadin kwayoyin halitta waɗanda ke tasowa ta hanyar maye gurbin kuma ana samun su a wuri ɗaya akan chromosome. A wasu kalmomi, alleles nau'i ne daban-daban na kwayoyin halitta iri ɗaya waɗanda zasu iya samar da bambancin daban-daban a cikin wani hali ko hali. Misali, kwayar halittar ido don launin ido yana da nau'ikan alloli masu yawa waɗanda ke samar da inuwar launuka daban-daban na launin ruwan kasa, shuɗi, kore, da sauransu. phenotype.