Transcript Notes About Variation in Pops

Remember, environments ALWAYS
change over time.
SPI 0807.5.3
Science
Variation
in Populations
So Notes
organisms also have
to change
(adapt) in order to
survive.
Variation in populations enables organisms to change (adapt).
Instructions
1) The process that drives variation…
1) First click on…"View"
from
the top-menu
is called
natural
selection bar.
2) Then click on "Slide Show" from the drop-down menu.
2)3)
Changes
andthe
variation
result from…
Then use
right-arrow
button on your keyboard to
…sexual
reproduction (over many generations)
advance through
this presentation.
3) Changes and variation also result from…
…genetic mutations (over many generations)
Organisms adapt by either changing their behavior or
changing their body structure or BOTH.
SPI 0807.5.3
Variation in Populations
Notes
Science
From Brown Bear to Polar Bear:
The Origin of Polar Bears
Species Name:
Ursus Arctos
Species Name:
Ursus Maritimus
Notes
SPI 0807.5.3
Variation in Populations
Science
From with
Brown
to White
Our story begins
twoBear
Brown
BearsBear:
living in the
Thewilderness
Origin of about
Polar Bears
Northern Canadian
70,000 years ago.
…one male …and one female
f
Let's call him "Jack"
Let's call her "Jill"
SPI 0807.5.3
Notes
Science
Jack and JillVariation
fell in love
one spring and mated.
in Populations
About 7 months later, Jill gave birth to four male cubs.
Jack
Jill
Dad
Mom
Moe
Larry
Curly
Shemp
Light Brown
Dark Brown
Dark Brown
Light Tan
Genes have pairs of allelesSPI
which
determine physical traits.
0807.5.3
Notes
Science
Variation
in Populations
In this case the alleles
determine
the color of the bear's fur.
Dominant allele B will result in brown fur.
Recessive allele b will result in tan fur.
3 cubs will have
brown fur
B b
B BB Bb
b Bb bb
(Brown)
(Brown)
(Tan)
(Brown)
Punnett Square
1 cub will have
tan fur
In their local habitat there
a population of 50 bears.
SPIwas
0807.5.3
Notes
(25Variation
males and
25 females)
Science
in Populations
Each mating pair had 4 cubs.
There were 100 cubs born (25 mating pairs x 4 Cubs=100)
Three cubs were brown, and one cub was tan.
There were 75 brown cubs
There were 25 tan cubs
For thousands of years brown fur provided the best
camouflage in the Canadian forests.
Yet environments ALWAYS change over time.
The winters came sooner and lasted longer, and the glaciers
began to move southward.
It was the start of a new Ice Age
SPI 0807.5.3
In the new white environment
brown fur was a disadvantage.
Notes
Variation in Populations
Science
Light colored fur became an advantage.
Many
the brown
bears Bear:
died.
FromofBrown
Bear fur
to White
The Origin
of thrived
Polar Bears
Yet the light colored
bears
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
SPI
0807.5.3 survival advantage in
The
lightest
color
bears
had
a
significant
Notes
Science
Variation in Populations
this new Ice Age environment.
Over time
lighter
colored
became
the norm.
From
Brown
Bearfur
to Polar
Bear:
The Origin of Polar Bears