module d: unit 3/lesson1 artificial selection and ...€¦ · corn began as a grass called teosinte...
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Module D: Unit 3/Lesson1
ARTIFICIAL SELECTION AND SELECTIVE BREEDING
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
Aim: What is artificial selection?
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 were easier to grind
• Some kernels tasted better
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.
Modern cornTeosinte
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?
14th century
print of a hunt.
Can you spot
the sight-
hounds?
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 SheepdogDo 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.
Biotechnology ( pg. 150)
• Bio = life
• Technology = use of scientific discoveries to implement solutions.
• Biotechnology is the use of biologicalunderstandings 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?
2. let only these cows reproduce
4. let only these offspring reproduce
5. keep repeating the process of selection and breeding until you achieve your goal.
3. select the offspring that produce the most milk
1. choose or select the cows in your herd that produce the most milk
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.
Artificial Selection In Animals
Let’s look at the history of where cows
came from….
The Auroch – is where all domesticated
cattle were bred from
Meat
Dairy
Draft
What was the “desired trait”?
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:
• Alters “natural evolution”; Interferes with an organisms natural ability to change overtime in order to adapt to changing environments
• Usually involves inbreeding, which can lead to reduced genetic diversity
• 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
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.
Artificial Selection
Ancient methodof genetic engineering
Nature does NOTcontrol thepassing on of traits to offspring
Reproduction isunder thecontrol of humans
Summary…..
There arebenefits alongwith problems
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