Selective breedingMonday, 30 March 2020

Keywords

4.8 – Explain selective breeding and its impact on food plants and domesticated animals.

ion ect cialSel Art Ss breifi ed Cro

Starter Rewrite the key words that you need to use when explaining natural selection:

VariationAdvantageous characteristicSurvivalReproductionHeritable

Selective breeding-Selective breeding (also known as artificial selection) is done intentionally.

-Organisms with desirable characteristics are “encouraged” to reproduce to pass on and enhance the characteristic to their offspring

About 8000 yrs ago people started to look for wild sheep that were naturally hairier than others and to breed them together. They then repeated this over

and over again, eventually ending up with woolly sheep.

Selective breeding-For selective breeding to be successful, to conditions are needed:There is variation in the populationThe characteristics are heritable

Example: selective breeding

Over time farmers have bred pigs to be longer and longer.This is because longer pigs have longer backs…Longer backs means more bacon…More bacon per pig means more profit!!

Old breed:Oxford Sandy and Black

New breed:British landrace

How’s it done?Stage 1: Farmer identifies his longest male and female pigs

Stage 2: Encourage the long pigs to mate

Stage 3: Encourage offspring of different parents to mate

Result: pigs become longer and longer.

Example: selective breeding

The same has been done with dogs.All dogs are descended from the wolfSelective breeding has resulted in dogs with different characteristics and jobs.

Can you match the dog to it’s role?

Bred to retrieve prey thathas been shot out of the air.They have rounded teethwhich prevents harm to thebird.

Bred to retrieve prey thatwas shot over water. Theyneed to be able to survivecold temperatures.

This dog is great for badgerhunting as it can fit easilydown holes to attackbadgers.

Dogs that herd sheep needto be agile, quick and veryintelligent.

Sheep dog

Golden retriever

Daschund

Poodle

Example: selective breeding

Plants have been selectively bred for a variety of reasons:1. Flavour2. Yield (how much

useful product they make.)

3. Growth speed4. Texture5. Disease resistance6. Coping with certain

environmental conditions.

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Question: State the alternative name for “selective breeding”

Question: Explain how a farmer could improve the amount of milk his farm produces by using selective breeding.

Question: Identify factors that farmers would want to see in a) Animals e.g. pigsb) Plants

Question: Complete the selective breeding in cows worksheet.

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Artificial selection

a) long backs, large amount of meat production, disease resistant, flavour, speed of growth

b) disease resistant, flavour, speed of growth, texture, yield

Answers

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Farmer identifies females that produce large amounts of milk (1)Identify males whose mother produces large amounts of milk (1)Breed these groups together (1)Repeat over many generations (1)

1) Gertrude and Rufus2) Penelope and Rufus3) Betsy and Boris4) Donald and Alma

The advantages to selective breedingSelective breeding is important in

agriculture:

1. Farmers can maximize yields and produce better quality products.

The process can also have medical uses:

2. Exploring reasons behind alcoholism. Rats have been bred

with either a strong or weak preference for alcohol. This allows

researchers to compare the different in behavior and brain

function.

The downside to selective breeding

There are risks associated with genetic breeding:• Animal welfare• Genetic defects• Inadequate genetic variation

Animal welfareTraits are chosen to benefit humans, not the animal.

Some selectively bred chickens produce so much breast meat they can’t stand up

Inadequate genetic variation

By selectively breeding animals, you make the individuals in a population very genetically similar.

Alleles are lost which may be useful in future if conditions change e.g.Temperature/climateDiseases

If they are all genetically similar then they will all be affected.

Genetic defectsWhen the gene pool is smaller, organisms are more likely to inherit genetic defects – traits which cause ill-health.

Daschunds –epilepsy

Bull dogs -Heart disease

German shepherds – hip dysplasia

Pugs can suffer from breathing problems.

Nearly half of all bananas are one variety.

They all have extremely similar DNA to each other.

A fungus is now threatening to destroy them all.

Inadequate genetic variation

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Question: what is an allele?

Suggest why scientists now save the seed of thousands of different plant varieties in seed banks.

Why does it matter if alleles are lost from a species?

In the 1840s, many Irish families grew one variety of potato for food. Suggest why a disease (potato blight) caused mass starvation in Ireland at this time.

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A version of a gene

To keep a history of available allelesWhich can be introduced in futureIf conditions change

The allele may be useful in future if conditions change

All the potatoes grown were gentically similarLittle variationPotato blight affected all of the potatoesSpread very quickly

PlenaryDo you think selective breeding is good or bad?

The most convincing argument wins a house point.