A Year at Brookfield Commons
1Emeka Haugland's sixth-grade science club spends a year studying Brookfield Commons, a city park with lawns, a weedy lot beside the parking area and a community center. The park, the people and the numbers here are made up, but they are based on real studies.
2In spring and early summer, the club studied two common weeds from the lot: dandelions and chicory. Both have flower heads made of many tiny flowers, and each tiny flower can make one seed. In many plants, a seed forms only after pollen reaches the flower and a sperm cell joins an egg cell, so the seed gets genetic information from two parents. Chicory works this way, and its flowers usually need pollen from a different chicory plant. To test the plants, the club's adviser, Ms. Henrietta Vos, used small scissors to slice the top off closed flower heads. Slicing removes the parts that make and catch pollen but leaves the bottom of the head, where seeds grow. After the tiny flowers had closed, the club tied a mesh bag over each head to catch its seeds.
3In June, the club planted 24 seeds from a sliced head of one dandelion plant, D1, and 24 seeds from one chicory plant, C1, whose flowers had been visited by bees carrying pollen from other chicory plants. All 48 seeds went into the same garden bed by the community center, with the same soil, sun and watering. Ten weeks later, the club compared the young plants.
4A pigeon club keeps a loft beside the community center, and in the fall its members showed Emeka their breeding records. Pigeon pairs usually raise two young, called squabs, at a time, several times a year. In these pigeons, wing pattern is controlled by one gene with two alleles. The checker allele (C) gives a checkered pattern and is dominant over the bar allele (c), which gives two dark bars across each wing. Each parent passes one of its two alleles, chosen at random, to each squab.