▁ 1 3 % ▁are ▁on ▁different ▁chrom os om es ▁or ▁on ▁dist antly ▁spac ed ▁lo ci . ▁ 1 7 2 ▁sub famil ies ▁of ▁OR ▁gen es ▁have ▁been ▁found ▁in ▁humans , ▁each ▁at ▁its ▁own ▁lo ci . ▁Because ▁the ▁gen es ▁in ▁each ▁of ▁these ▁sub famil ies ▁are ▁struct ur ally ▁and ▁function ally ▁similar , ▁and ▁in ▁close ▁proxim ity ▁to ▁each ▁other , ▁it ▁is ▁hypoth es ized ▁that ▁each ▁evol ved ▁from ▁single ▁gen es ▁under going ▁dup lication ▁events . ▁The ▁high ▁number ▁of ▁sub famil ies ▁in ▁humans ▁explains ▁why ▁we ▁are ▁able ▁to ▁recognize ▁so ▁many ▁od ors . ▁ ▁Human ▁OR ▁gen es ▁have ▁hom olog ues ▁in ▁other ▁m amm als , ▁such ▁as ▁m ice , ▁that ▁demonstrate ▁the ▁evolution ▁of ▁Ol factory ▁Re ceptor ▁gen es . ▁One ▁particular ▁family ▁that ▁is ▁involved ▁in ▁the ▁initial ▁event ▁of ▁od or ▁per ception ▁has ▁been ▁found ▁to ▁be ▁highly ▁conser ved ▁throughout ▁all ▁of ▁verte br ate ▁evolution . ▁ ▁D ise ase ▁ ▁Dup lication ▁events ▁and ▁redundant ▁gen es ▁have ▁often ▁been ▁thought ▁to ▁have ▁a ▁role ▁in ▁some ▁human ▁dise ases . ▁Lar ge ▁scale ▁whole ▁gen ome ▁dup lication ▁events ▁that ▁occurred ▁early ▁in ▁verte br ate ▁evolution ▁may ▁be ▁the ▁reason ▁that ▁human ▁mon ogen ic ▁disease ▁gen es ▁often ▁contain ▁a ▁high ▁number ▁of ▁redundant ▁gen es . ▁Chen ▁et ▁al . ▁hypoth es izes ▁that ▁the ▁function ally ▁redundant