Artificial Selection Breeding for a purpose All our modern breeds of dog are descended from the...
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Transcript of Artificial Selection Breeding for a purpose All our modern breeds of dog are descended from the...
So how come they all look and act so differently?
Loyal and intelligent
Small and friendly
Large and strong
Hard-working with a thick coat
Courageous, with a very strong jaw
Very fast and agile
Gamekeepers in the 1800s had a problem. Poachers were entering their land and stealing their game-birds before the shooting season. Their dogs (mastiffs) were big, strong dogs and great companions but they were not aggressive or fast enough to chase after the poachers.
Mastiff Bulldog
Another breed known to them was the bulldog. This was quick and aggressive but not strong enough to pull the poachers down and hold them until a gamekeeper arrived.
What could they do?
Humans have changed the way dogs look and act by choosing which dogs to breed together.
Mastiff – large and strong but slow and not aggressive.
Bulldog – Aggressive and quick but small.
Bullmastiff – Large, quick, strong and aggressive
This is called
Selective Breeding
Perfect!
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This dog is a more modern example of selective breeding.
It is a relatively new breed called a labradoodle.
What two dogs do you think were bred to make it?
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?
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 more than 3000 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
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
Would it be right to selectively breed humans??
• Adolf Hitler believed in a master race (the Aryans) and implemented a plan to create this race.
• This involved eugenics – the selective breeding of humans.
Nazi eugenics
• Those considered “not worthy of life”, - let alone allowed to have children - included (but was not limited to) the criminal, degenerate, dissident, feeble-minded, homosexual, idle, insane, and the weak
• 400,000 people were sterilised against their will and 70,000 were killed