Module D: Unit 3/Lesson1
Artificial Selection Selective Breeding
Aim: What is artificial selection? Objective: Explain how artificial selection influences the inheritance of traits in organisms Explain how humans have manipulated traits in various organisms to acquire desired traits
Scientists recently analyzed the DNA of dogs. They identified the common ancestor of ALL dogs. Can you guess which animal is the ancestor of the dog?
Artificial Selection or Selective Breeding the breeding of plants and animals to produce desirable traits people select certain organisms to reproduce in order to obtain offspring that inherit ONLY the desired features
Dogs bred for a purpose Dogs have been selectively bred for a purpose for over 14,000 years How many breeds of dogs currently exist? Currently there are over 400 breeds of dogs. All descended from the wolf.
Dogs bred for a purpose Dogs have been selectively bred for a purpose for over 14,000 years Starting with some wolves, dogs were initially bred to help with: Hunting; producing sight hounds, scent hounds, terriers, and retrievers
Afghan hound
Dogs bred as sighthounds - clockwise from top left: Whippet, Borzoi, and Saluki Observe and record the similarities in their anatomy. What physical characteristics do you think were selected?
14 th century print of a hunt. Can you spot the sighthounds? How did you identify them?
Dogs bred for a purpose Farming; producing herding dogs and guard dogs
German Shepard
Great Dane
Dogs bred for a purpose Farming; producing herding dogs https://www.youtube.com/watch?v=2hpmlmw5w5u
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 Modern breeding has given us companion dogs and toy dogs whose purpose is to keep us company. What characteristics would be desirable in companion dogs? What characteristic common in all toy breeds of dog?
All 400 dog breeds are the product of artificial selection!
Let s look at the history of where cows came from.
The Auroch where all domesticated cattle were bred from
Suppose you wanted a variety of cow that produced a lot of milk. How do we get to our goal? 1. Select the cows in your herd that produce the most milk 2. Let only these cows reproduce 3. Select the offspring that produce the most milk 4. Let only these offspring reproduce 5. Keep repeating the process of selection and breeding until you achieve your goal.
What was the desired trait? Identify the desired trait. How do you know?
What was the desired trait? Identify the desired trait. How do you know? Meat Dairy Draft
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 able to survive nasty weather Q: What do you think happened when the two types were cross-bred?
Q: What do you think happened when the two types were crossbred? A: A dwarf wheat with high yield that was able to survive nasty weather.!
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 Alters natural selection ; Interferes with an organisms natural ability to change overtime in order to adapt to changing environments
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 again This is repeated over several generations until the desired trait is fully developed
Artificial Selection Nature does NOT control the passing on of traits to offspring Reproduction is under the control of humans Ancient method of genetic engineering There are benefits along with problems
How would you? Discuss how you would breed for: Better quality ( higher milk fat) milk from cows - Increased amount of wool in sheep