Graphic error and simple list

import matplotlib.pyplot as plt
x=[]
y=[]
z=[]
dados=open('dados1.txt','r')
for line in dados:
    line=line.strip()
    X,Y,Z=line.split()
    x.append(X)
    y.append(Y)
    z.append(Z)
dados.close()
plt.plot(x,y,'o')
plt.plot(x,z,'o')
plt.show()

I made a program that collects data from a txt file and generates a graph, but generating the y-axis is odd.