# calculate all the principal components (4)
X = female_df[['father', 'mother', 'father_sqr', 'mother_sqr']].values
y = female_df['childHeight']
pca = PCA()
pca_result = pca.fit_transform(X)
pca_df = pd.DataFrame(data = pca_result, columns=['pc1', 'pc2', 'pc3', 'pc4'])