▁then ▁benef icial ▁tra its ▁will ▁occur ▁both ▁before ▁and ▁after ▁reprodu ction ▁due ▁to ▁natural ▁selection . ▁This , ▁however , ▁is ▁not ▁observed ▁in ▁nature , ▁and ▁thus ▁ant agon istic ▁ple iot ropy ▁cont ributes ▁to ▁the ▁slow ▁d eter ior ation ▁with ▁age ▁( sen esc ence ). ▁ ▁Mechan ism ▁P lei ot ropy ▁describes ▁the ▁gen etic ▁effect ▁of ▁a ▁single ▁gene ▁on ▁multiple ▁phen ot yp ic ▁tra its . ▁The ▁underlying ▁mechanism ▁is ▁gen es ▁that ▁code ▁for ▁a ▁product ▁that ▁is ▁either ▁used ▁by ▁various ▁cells ▁or ▁has ▁a ▁cas cade - like ▁signal ing ▁function ▁that ▁affect s ▁various ▁targets . ▁ ▁Mod els ▁for ▁the ▁origin ▁ ▁One ▁basic ▁model ▁of ▁ple iot ropy ' s ▁origin ▁describes ▁a ▁single ▁gene ▁loc us ▁to ▁the ▁expression ▁of ▁a ▁certain ▁trait . ▁The ▁loc us ▁affect s ▁the ▁expressed ▁trait ▁only ▁through ▁changing ▁the ▁expression ▁of ▁other ▁lo ci . ▁Over ▁time , ▁that ▁loc us ▁would ▁affect ▁two ▁tra its ▁by ▁interact ing ▁with ▁a ▁second ▁loc us . ▁D irection al ▁selection ▁for ▁both ▁tra its ▁during ▁the ▁same ▁time ▁period ▁would ▁increase ▁the ▁positive ▁correlation ▁between ▁the ▁tra its , ▁while ▁selection ▁on ▁only ▁one ▁trait ▁would ▁decrease ▁the ▁positive ▁correlation ▁between ▁the ▁two ▁tra its . ▁Event ually , ▁tra its ▁that ▁under w ent ▁direction al ▁selection ▁simultaneously ▁were ▁linked ▁by ▁a ▁single ▁gene , ▁resulting ▁in ▁ple iot ropy . ▁ ▁Other ▁more ▁complex ▁models ▁compens ate