GCSE · Biology · Edexcel · Spec 1BI0

Selective breeding

Cabbage, kale, broccoli and cauliflower look nothing alike. Yet they're one species, and humans made them different on purpose. Here's how.

Breed a better wheat

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Parent 1 · 1/8scrub through the generations →

Borlaug's first choice: a tall variety of wheat that produced lots of grain. Great grain, but it's tall. He picks it on purpose, for the grain.

Norman Borlaug wanted wheat with lots of grain AND a short, thick stem. No plant had both. Scrub through and watch him get there.

Why short wheat mattered

?

Reason it through

How did breeding short, thick-stemmed wheat help feed millions of people?

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First link · your turn

Start with the old wheat. What went wrong with tall plants?

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What do we breed for?

Crops, animals, or both?

For each feature, tick where selective breeding has been used to get more of it: in crops, in animals, or in both.

  • A Crops (plants)
  • B Animals
  1. A bigger edible part
  2. Better taste
  3. More nutritional value or calories
  4. Resistance to pests
  5. A shorter growing time
  6. Growing in poorer quality soil
  7. More muscle, so more meat
  8. More eggs, wool or milk
  9. Pulling heavy farm equipment
  10. Herding other farm animals
  11. Smaller horns, or no horns
  12. Easier or safer to farm

How far can a species change?

One wild plant, four vegetables

Choose which part of the wild plant the breeders enhanced, then follow the branch to a vegetable.

Part the breeders enhanced → Vegetable

  • The wild ancestor. Every vegetable below is descended from it.

4 vegetables from one wild plant.

On Wild mustard (wild cabbage). 2 branches to choose from.

Cabbage, kale, broccoli and cauliflower look like four different vegetables. They are all one species, Brassica oleracea, made very different by selective breeding.

What do you think?

From wolf to pet dog

Pet dogs are descended from wolves. Cattle were bred from the aurochs, a large, aggressive wild animal that is now extinct. The domesticated animals are very different from their wild ancestors. Three students explain how that happened.

Which is closest to what you think right now?
How sure are you?

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

That's selective breeding: pick parents with the feature you want, breed them, keep the best offspring, and do it again, generation after generation.

What you need to know

  • Selective breeding: humans choose organisms with desirable features and breed them to produce offspring with those features.
  • It can be carried out on both plants and animals.
  • The steps: select two parents with the desired characteristics, breed them, select the offspring with the characteristics, breed those, and repeat for several generations until all the offspring have them.
  • The choice is deliberate, not random. Crops are bred by cross pollination; for animals, artificial insemination can be used.
  • Selective breeding has improved food security, for example through Norman Borlaug's short-stemmed, high-grain wheat.

The big picture

Selective breeding is when humans choose organisms with features they want and breed them to get offspring with those features. It works on plants and animals. You select two parents, breed them, select the best of the varied offspring, breed those, and repeat for several generations until all the offspring have the feature. Crops are bred by cross pollination; for animals, artificial insemination can be used. Over many generations a species can change a lot, and selective breeding of crops such as wheat has greatly improved food security.

Key points

1Humans, not chance, decide which individuals breed, and they choose for features that are useful to us: food, materials or work.
2Offspring vary, so one round of breeding is never enough. The select-and-breed loop repeats over many generations.
3Cross pollination: pollen from one chosen plant is transferred to another.
4Artificial insemination: semen is taken from a male animal and inserted into the female, so the chosen pair really do reproduce.
5After many generations a species can look very different from its wild ancestor: wolves to pet dogs, the aurochs to cattle, wild mustard to cabbage, kale, broccoli and cauliflower.
6Food security is a measure of the quantity and quality of food available to households or communities. A shortage can lead to poor health and starvation.
7Borlaug's wheat was part of the Green Revolution, which massively increased crop yields and saved millions of people from starvation.

Worked example

Problem

A sheep farmer wants a flock in which every sheep produces lots of wool. Describe how the farmer could use selective breeding to get this.

⚠ Watch out

Describing selective breeding as a single pairing, for example 'breed two woolly sheep and the lambs will all be woolly'. The offspring vary, so you have to select the best offspring and breed them again, over several generations, until all the offspring have the feature.

🧠

Memory hook

Pick, pair, pick again. Pick the parents, pair them up, pick the best of the babies, and keep going until every baby has it.

✓

Check yourself

Cover the page. Can you put the steps of selective breeding in order, say what cross pollination and artificial insemination are, and explain how short-stemmed wheat helped more people get enough food?

Flashcards

(13)
What is selective breeding?
Humans choosing organisms with desirable features and breeding them to produce offspring with those features.
Is selective breeding used on plants, animals or both?
Both. Crops and animals can be selectively bred.
Why isn't selective breeding random?
Humans make a very deliberate choice about which individuals breed.
What is cross pollination?
Transferring pollen from one plant to another. It's how chosen crop plants are bred together.
What does artificial insemination involve, and why use it?
Semen is taken from a male animal and inserted into the female. It makes sure the chosen male and female are the ones that reproduce.
When does a breeder stop repeating the select-and-breed step?
When all the offspring have the desired characteristic.
What do cabbage, kale, broccoli and cauliflower have in common?
They are all descended from wild mustard and are the same species, Brassica oleracea.
Which animals have been bred to do work?
Cattle and horses to pull heavy farm equipment, and dogs such as collies to help herd other farm animals.
What were pet dogs bred from, and for what features?
Wolves. They were bred to be less aggressive and more obedient.
What is food security?
A measure of the quantity and quality of food available to households or whole communities.
What was the problem with tall wheat?
The wind knocked it over, so the grain fell to the ground and could rot or be eaten before harvest.
Which two wheat varieties did Norman Borlaug breed together?
A tall variety with lots of grain and a dwarf variety with a shorter, thicker stem.
Which staple crops provide most of the energy humans need?
A small number of crops such as rice, wheat and corn, all selectively bred to increase food production.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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