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