All quarks carry a baryon number B = ⁠+ + 1 / 3 ⁠ , and all anti-quarks have B = ⁠− + 1 / 3 ⁠ . They also all carry weak isospin, T 3 = ⁠± + 1 / 2 ⁠ . The positively charged quarks (up, charm, and top quarks) are called up-type quarks and have T 3 = ⁠+ + 1 / 2 ⁠ ; the negatively charged quarks (down, strange, and bottom quarks) are called down-type quarks and have T 3 = ⁠− + 1 / 2 ⁠ . Each doublet of up and down type quarks constitutes one generation of quarks.