Foods People Have Changed
1Mr. Kwame Sorensen-Díaz's food science class at Harmon Ridge Middle School spent one week on foods that people have changed. On Monday the class pressed corn tortillas. Then he passed around two ears: a long ear of field corn and a thin ear of teosinte, no longer than a finger, from a seed collection. Teosinte is a wild grass that still grows in Mexico. DNA studies show that corn was bred from teosinte about 9,000 years ago by farmers in what is now southern Mexico.
2For thousands of years, farmers saved seeds from the plants they liked best at each harvest and planted them the next season. Plants of the same kind differ a little in almost every trait. Some teosinte ears had a few more kernels than others, some had thinner kernel cases, and some held together a little longer when ripe. Table 1 compares teosinte with corn today.
3On Wednesday, Bettina Aroyo's group tested apples. When an apple is cut, an enzyme from its cells mixes with oxygen from the air and turns the cut surface brown. The group cut slices from a regular apple and from a non-browning apple of the same variety. To make the non-browning apple, scientists added a piece of DNA to the apple tree's cells that switches down the tree's own genes for the browning enzyme. New trees grafted from the engineered tree also grow non-browning apples. Mr. Sorensen-Díaz cut all of the slices at the same time so that every group started together. The group also dipped some regular slices in lemon juice, a common kitchen trick. All of the slices sat on plates at room temperature, and the group scored browning from 0 (none) to 5 (fully brown). Table 2 shows the average score of six slices in each group.
4On Friday the class read about golden rice. Rice plants make beta-carotene, an orange substance the body turns into vitamin A, in their green leaves but not in their grain, and plant breeders have not found any rice plants that store it in the grain. So scientists added two genes to rice, one from corn and one from a soil bacterium. The grains of golden rice are yellow-orange because they hold beta-carotene. In places where people eat mostly rice, too little vitamin A can harm children's eyesight.