Questions: Artificial Selection and Selective Breeding

Question 1

Broccoli, cabbage, kale and cauliflower look very different. What do they have in common?

• A. They come from four different wild plants
• B. They were all bred by people from one wild mustard species
• C. They are the same plant grown in different soils
• D. They were made by genetic engineering in the last 50 years

Answer: (B)

All of these vegetables belong to the species Brassica oleracea. Farmers over many centuries selected different parts of the wild plant: large leaves for kale, a tight leaf bud for cabbage, and flower clusters for broccoli and cauliflower.

Question 2

A farmer can breed a cow that gives purple milk as long as she keeps selecting for it, even if no cow has ever had any trace of that trait.

• T. True
• F. False

Answer: False

Selection can only act on heritable variation that exists. If no cow carries genes for purple milk, choosing parents cannot produce it. Breeders can only make existing traits more common or more extreme.

Question 3

How is artificial selection similar to natural selection, and how is it different?

Model answer: In both, individuals with certain heritable traits reproduce more, so those traits become more common over generations. In artificial selection people choose which traits are favored; in natural selection the environment does, by affecting which individuals survive and reproduce.

Charles Darwin used this comparison in On the Origin of Species (1859), whose first chapter discusses variation in domesticated animals and plants such as pigeons, before he turned to natural selection.

Question 4

Corn (maize) was bred from a wild grass called teosinte. What did early farmers most likely do?

• A. They planted seeds only from plants with the largest, most useful ears, generation after generation
• B. They waited for teosinte to change by itself in one year
• C. They mixed teosinte with wheat to make corn
• D. They grew teosinte in the dark

Answer: (A)

By saving and planting seeds from the plants with the traits they liked, such as larger ears and kernels that stayed on the cob, farmers in what is now Mexico gradually turned teosinte into maize over thousands of years.