pI values for the nine major milk proteins in 13 mammalian species compared to the pI of the human proteome. The top histogram represents the pI distribution of the human proteome. The histogram's x-axis is shared with that of the major milk proteins' pI shown below. The Colors indicate the different milk proteins. The tree on the left is the mammalian species tree from Benton and Donoghue . Two extra pI values are represented between brackets at the opossum level, these represent the pI of the reported extra copies of κ-casein this species possess . The values are for the proteins with the accession numbers FJ548612 and FJ548626 respectively.