The X and Y Chromosomes Determine Your Sex. One chromosome pair - the sex chromosomes - is unique. You don't necessarily end up with a matching pair. Typically females have two X chromosomes and males have an X and a Y. Mothers always pass an X chromosome on to their children.
On the other hand, the absorption of nonheme iron, the major dietary pool, is greatly influenced by meal composition. Ascorbic acid is a powerful enhancer of nonheme iron absorption and can reverse the inhibiting effect of such substances as tea and calcium/phosphate.
Calcium is absorbed and excreted over 12 hours: The vitamin C discovery was followed by a study showing calcium is absorbed over a 12 hour period, preferably in small doses from 200-400 mg (Urinary Excretion of Calcium in Students and Mature Women Taking Supplements, A. Cone, T. Danner, and A. B. Ordman, AGE 19(4): 164 (1996)