Aphid Clones and Tomato Crosses

Two Kinds of Families in the Greenhouse

1The greenhouse club at Westbrook Middle School grows peppers and tomatoes in a small glass greenhouse behind the gym. In June, seventh grader Jonah Feldman found tiny green aphids on the underside of a pepper leaf. Aphids are insects that suck sugary sap from plants. The club's advisor, Ms. Adaeze Obi, asked the club to count the aphids on that plant every four days.

2Ms. Obi explained that in summer, a colony of this kind of aphid is usually made up of females only. Each female gives birth to live young without mating. The young develop from the mother's own cells, so they get all of their genetic information from her. Under a hand lens, the aphids on the pepper plant looked alike in size, color and shape. In the fall, the colony will produce males and females that mate, and the females will lay eggs that can survive the winter.

3The club also breeds tomatoes. In the tomato variety they grow, the allele R for red fruit is dominant, and the allele r for yellow fruit is recessive. To make a cross, students move pollen from the flower of one plant to the flower of another with a small paintbrush. Each seed that forms gets one allele from each parent plant. The students planted the seeds from three crosses, grew the seedlings and recorded the fruit color of each plant.

4For Cross 3, the club used a red-fruited plant they called Plant X. They did not know whether Plant X had the genotype RR or Rr, so they crossed it with a yellow-fruited plant (rr) to find out.