Nature: 1; Nurture: 0

• The gene variant that influences whether children learn from their mistakes. With the misspelled gene, brains have about 30 percent fewer dopamine receptors and less activity in the brain's frontal cortex (the site of higher-order thinking, including monitoring negative feedback) and hippocampus (memory) than do people with the more common form of the gene. In an experiment at the Max Planck Institute for Neurological Research in Germany, people with the misspelling weren't able to avoid choices that they were told over and over were incorrect. Numerous other studies have linked this gene variant to addiction, obesity and compulsive gambling, suggesting that the underlying problem is trouble learning the negative consequences of your actions.

• The DNA variant that affects whether a baby's brain development will be spurred by breast-feeding, which has been reported to confer an extra half-dozen or so IQ points by kindergarten. But not all breast-fed babies are little Einsteins, making their mothers wonder why all the milk-stained blouses didn't seem to boost cognitive development. The reason seems to be that there are two forms of a gene called FADS2. In the 90 percent of babies who carry the "C" form, breast-feeding raises intelligence by an average of nearly seven IQ points, scientists led by Terrie Moffitt and Avshalom Caspi of Duke University reported last year. This version of FADS2 produces an enzyme that helps convert the fatty acids in breast milk into compounds that help signals zip along brain neurons and spur neurons to sprout connections, which underlie intelligence, memory and creativity. The 10 percent of babies who carry the other form of the gene lack the enzyme and therefore derive no cognitive benefit from breast-feeding (though they still get an immune-system boost from it).

• DNA variants can protect children from bad parenting