Plant and animal breeding

Maria and Sofia are in a park, when Sofia notices a wild apple tree. Maria, apples! Why are they so tiny? The apples are red and they look ripe. But they are indeed quite small, and not as pretty as the apples in shops.

Why are these wild apples so different? When we shop for fruits and vegetables, of course we prefer those that look good and taste delicious. Farmers want their crops to grow well and be resistant to harsh conditions, diseases or pests. Farmers also want their animals to produce a great deal, say, eggs, or milk, or wool, or to grow fast, so that farmers can sell and make a profit. But how can we be sure that plants and animals will have these desired traits?

Let’s go back a few thousand years. Thousands of years ago, humans don't farm — they simply pick the easiest-to-access, sweetest and largest fruit they come across. Any fruit humans eat means they spread seeds, and so more desirable plants with these nice traits grow. In time, humans start to keep animals, such as goats or sheep. Animals that are weak, prone to sickness, or very stubborn are not useful, so farmers tend to remove these from their herds.

Only strong, healthy and well-behaved animals are left to reproduce. Over time, people notice that many traits get passed on from parents to offspring, both in plants and in animals. So farmers start to select seeds to sow from the best plants, and the best animals from their herds to mate and breed. This is called selective breeding. Through selective breeding, generation after generation, humans manage to change the characteristics of different species, to better suit the needs of humans.

Corn, peaches, and apples, for example, are plants that have been selectively bred over thousands of years. All these crops used to be much smaller and less tasty, but now come in a number of delicious varieties! Different breeds of dogs and farm animals have also been created through selective breeding throughout history! Today we know that traits of different plants and animals are determined by genes. Plants or animals that have similar genes also look alike.

Offspring inherit genes from their parents. But in each generation, there is usually some variation, and offspring are not identical to their parents. So through selective breeding humans can create new varieties of animals and plants, with good traits from both parents. What if we already have a variety with all the perfect qualities, and we just want greater numbers of it? To do that, we need to ensure that any new plant or animal has identical genes to the one we want.

This is achieved through cloning. Cloning plants is relatively easy. If you cut off a part of a plant, the new part can often grow its own new roots, stems and leaves. It becomes a new plant that has exactly the same genes as the parent plant. Growing plants in this way allows us to consistently produce plant clones that have identical genes and characteristics.

Cloning animals is possible too, but it’s difficult and not practical. Selective breeding remains the main method of maintaining and enhancing desired traits in animals. Both selective breeding and cloning allow us to produce plants and animals that have desired traits. But by focusing on certain traits, we might eliminate other qualities that are useful. For instance, trying to breed a brilliantly red apple, we might reduce the tree’s ability to survive in its natural environment.

Artificially bred individuals usually have very similar genes to each other. This means they have the same strengths but also the same weaknesses. They might have the same health issues or be prone to the same diseases. I bet this wild apple tastes delicious anyway!