Artificial Selection

Breeding for a purpose

Dogs bred as sighthounds -

clockwise from top left: Whippet,

Borzoi, and Saluki

Can you see the similarities in their

anatomy?

What physical characteristics do you

think were selected?

14th century

print of a hunt.

Can you spot

the sight-

hounds?

How did you

decide?

Dogs bred as herding dogs – clockwise

from top left – Border collie,

Lancashire heeler, Rottweiler, Old

English Sheepdog

Do you think the

characteristics that

are bred for are

physical or

behavioural?

Why?

Dogs – bred for a purpose

• Dogs have been selectively bred for a purpose for 15,000 years

• Starting with some wolves, dogs were initially bred to help with:

– hunting; producing hounds, terriers, and retrievers

– farming; producing herding dogs and guard dogs

• Modern breeding has given us companion dogs and toy dogs – whose purpose is to keep us company… funnily enough

Meat

Dairy

Draft

The Auroch – where all domesticated

cattle were bred from

Artificial selection in plants

Wheat

• Tall wheat plants have a high yield, but are easily damaged in wind and rain

• Dwarf wheat plants have a low yield, but are robust against nasty weather

• Q: What do you think happened when the two types were cross-bred?

• A: A dwarf wheat with high yield that was robust!

• Other types were produced, but they were discarded

• Discuss how you would breed for:

– Better quality of milk from cows

– - Increased number of

offspring in sheep

How would you…?

In summary…

• Selective breeding = Artificial selection

• Has been used for animals and plants

• The method:

– The desired characteristics are identified

– They are bred together

– Only the offspring exhibiting the desired

characteristics are bred

– This is repeated over several generations until

the desired trait is fully developed

In summary…

• Problems:

• Traits are chosen to benefit humans, not the animal

– Physical problems often occur in domestic animals eg. Inflammation of the udder (mastisis) in cows due to increased milk production

• Usually involves inbreeding, which can lead to reduced genetic diversity