b ▁mus cle ▁mass ▁as ▁its ▁primary ▁effect ▁( the ▁phen ot yp ic ▁effect ▁by ▁which ▁it ▁was ▁originally ▁identified ). ▁In ▁addition ▁to ▁smaller ▁h ind lim b ▁mus cle ▁mass , ▁the ▁mut ant ▁m ice ▁exhib it ▁lower ▁heart ▁rates ▁during ▁physical ▁activity , ▁and ▁a ▁higher ▁end urance . ▁M ini ▁Mus cle ▁M ice ▁also ▁exhib it ▁larger ▁kid ne ys ▁and ▁li vers . ▁All ▁of ▁these ▁morph ological ▁devi ations ▁influence ▁the ▁behavior ▁and ▁met abol ism ▁of ▁the ▁mouse . ▁For ▁example , ▁m ice ▁with ▁the ▁M ini ▁Mus cle ▁mut ation ▁were ▁observed ▁to ▁have ▁a ▁higher ▁per - gram ▁aer ob ic ▁capacity . ▁The ▁mini - mus cle ▁alle le ▁shows ▁a ▁m end elian ▁re cess ive ▁behavior . ▁The ▁mut ation ▁is ▁a ▁single ▁nucle ot ide ▁polym orphism ▁( SN P ) ▁in ▁an ▁intr on ▁of ▁the ▁my os in ▁heavy ▁pol ype pt ide 4 ▁gene . ▁ ▁Ch ick ens ▁▁ ▁Ch ick ens ▁exhib it ▁various ▁tra its ▁affected ▁by ▁ple iot rop ic ▁gen es . ▁Some ▁ch ick ens ▁exhib it ▁fri zz le ▁fe ather ▁trait , ▁where ▁their ▁fe athers ▁all ▁curl ▁out ward ▁and ▁up ward ▁rather ▁than ▁lying ▁flat ▁against ▁the ▁body . ▁Fri zz le ▁fe ather ▁was ▁found ▁to ▁stem ▁from ▁a ▁delet ion ▁in ▁the ▁genom ic ▁region ▁coding ▁for ▁α - K er atin . ▁This ▁gene ▁seems ▁to ▁ple iot rop ically