1) The process that drives variation…

2) Changes and variation result from…

3) Changes and variation also result from…

…sexual reproduction (over many generations)

…genetic mutations (over many generations)

… is called natural selection

Organisms adapt by either changing their behavior or changing their body structure or BOTH.

Notes SPI 0807.5.3

Variation in Populations

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ScienceRemember, environments ALWAYS change over time. So organisms also have to change (adapt) in order to survive.Variation in populations enables organisms to change (adapt).

Notes

From Brown Bear to Polar Bear:The Origin of Polar Bears

SPI 0807.5.3 Variation in Populations

Species Name: Ursus Arctos

Species Name: Ursus Maritimus

Science

From Brown Bear to White Bear:The Origin of Polar Bears

Our story begins with two Brown Bears living in the Northern Canadian wilderness about 70,000 years ago.

f

Let's call him "Jack"

…and one female…one male

Let's call her "Jill"

Notes SPI 0807.5.3

Variation in Populations Science

Dad Mom

Moe Larry Curly

Light Brown Dark Brown Light Tan

Jack Jill

Shemp

Dark Brown

Notes SPI 0807.5.3

Variation in Populations ScienceJack and Jill fell in love one spring and mated.

About 7 months later, Jill gave birth to four male cubs.

BBB b

B

b Bb

Bb

bb

Dominant allele B will result in brown fur.

Recessive allele b will result in tan fur.3 cubs will have

brown fur

1 cub will have tan fur(Brown)

(Brown)

(Brown)

(Tan)

Punnett Square

Notes SPI 0807.5.3

Variation in Populations ScienceIn this case the alleles determine the color of the bear's fur.

Genes have pairs of alleles which determine physical traits.

There were 75 brown cubs There were 25 tan cubs

Three cubs were brown, and one cub was tan.

There were 100 cubs born (25 mating pairs x 4 Cubs=100)

Notes SPI 0807.5.3

Variation in Populations ScienceEach mating pair had 4 cubs.

In their local habitat there was a population of 50 bears. (25 males and 25 females)

The winters came sooner and lasted longer, and the glaciers began to move southward.

It was the start of a new Ice Age

Yet environments ALWAYS change over time.

For thousands of years brown fur provided the best camouflage in the Canadian forests.

From Brown Bear to White Bear:The Origin of Polar Bears

Many of the brown fur bears died.

Yet the light colored bears thrived and multiplied.

Originally 75% were brown and 25% were light colored.

Over time this percentage reversed with 75% light colored and 25% brown..

Brown Fur Light Tan Fur

Notes SPI 0807.5.3

Variation in Populations ScienceIn the new white environment brown fur was a disadvantage.

Light colored fur became an advantage.

From Brown Bear to Polar Bear:The Origin of Polar Bears

Over time lighter colored fur became the norm.

Notes SPI 0807.5.3

Variation in Populations ScienceThe lightest color bears had a significant survival advantage in this new Ice Age environment.