Module D: Unit 3/Lesson1 ARTIFICIAL SELECTION AND 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
This was corn 10,000 years ago. TEOSINTE
This is corn today.
How did the plant on the left become the sweet corn we love today?
The corn plants we eat today trace their roots back about 10,000 years to the wild ancestors of corn that were quite different. Ancestor
Corn began as a grass called teosinte No cob, no husks, no kernels
Ancient farmers in Mexico took the first steps in domesticating corn.
These farmers noticed that not all plants were the same. Farmers noticed.. Some plants may have grown larger than others Some kernels tasted better Some kernels were easier to grind The farmers liked some of the traits and
The farmers saved the kernels from plants having these desirable traits and planted them for the next season's harvest.
Over time corn cobs became larger, with more rows of kernels, eventually taking on the form of the modern corn we eat today. Teosinte Modern corn
The sweet corn we know of today is the result of farmers over thousands of years planting seeds, studying the results, saving and sowing seeds only from corn plants they liked best
Sowing ONLY the corn seeds with the desired traits is called SELECTIVE BREEDING or ARTIFICIAL SELECTION.
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
It took many years before the corn we eat today ever came to exist
Getting the desired trait didn t happen in just one try. They had to repeatedly cross breed many generations until the desired traits fully developed.
Let s look at Artificial Selection in Dogs
There are about 400 different dog breeds we know of today. How did these dog breeds get here?
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?
All dog breeds are the outcome of artificial selection too! Dogs from other countries were brought here and selectively bred
Why were dogs selectively bred? video clip slide 4
Dogs bred for a purpose Dogs have been selectively bred for a purpose for 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 Can you see 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 Dogs have been selectively bred for a purpose for 14,000 years Starting with some wolves, dogs were initially bred to help with: farming; producing herding dogs and guard dogs
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 behavioral? Why?
Dogs bred for a purpose Dogs have been selectively bred for a purpose for 14,000 years Starting with some wolves, dogs were initially bred to help with: Modern breeding has given us companion dogs and toy dogs whose purpose is to keep us company.
Artificial Selection in Dogs. The Controversy
Bull Terrier Today s Bull Terrier has been seriously impaired by selective breeding. They suffer teeth problems as they now have too many teeth in their enlarged skulls. Their mentality has also been affected, as they are obsessed with chasing their tails
Basset Hound Basset Hound struggles with a host of problems resulting from selective breeding. They have far too much skin, suffer serious eye problems, and experience spinal problems.
Bio = life Biotechnology ( pg. 150) Technology = use of scientific discoveries to implement solutions. Biotechnology is the use of biological understandings to solve practical problems. Artificial selection is one example of biotechnology.
Let s Look at Artificial Selection In Animals
Suppose you wanted a variety of cow that produced a lot of milk. How would you accomplish doing this? 1. choose or 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.
Artificial Selection In Animals Farmers do exactly this. They allow ONLY the animals with desirable characteristics to reproduce. The HUMAN decides which cows will be the parents of the next generation.
Let s look at the history of where cows came from.
The Auroch is where all domesticated cattle were bred from
What was the desired trait? 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 robust ( not easily damaged) in 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
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
Problems: Traits are chosen to benefit humans, not the animal Physical problems often occur in domestic animals for example: -Passing on recessive genes that cause physical, mental & behavioral issues - Inflammation of the udder in cows due to increased milk production Usually involves inbreeding, which can lead to reduced genetic diversity Alters natural evolution ; Interferes with an organisms natural ability to change overtime in order to adapt to changing environments
Benefits: Improved Quality of Food Sources. Selectively breeding animals with higher protein and lower fat percentages, as well as plants that have higher nutritional values, you create food sources with a higher quality of nutrition.
Summary.. 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