Notes

1. Press the right arrow button to Advance through the Presentation! SPI 0807.5.3 Variation in Populations Notes  • Remember, environments always change over time. • So organisms also have to change (adapt) in order to survive. • Variation in populations enables organisms to change (adapt). 1) The process that drives variation… … is called natural selection 2) Changes and variation result from… …sexual reproduction (over many generations) 3) Changes and variation also result from… …genetic mutations (over many generations) When significant environmental changes occur, organisms must also change (adapt) by either changing their behavior or changing their body structure or both.

2. SPI 0807.5.3 Variation in Populations Notes  From Brown Bear to White Bear: The Origin of Polar Bears Species Name: UrsusMaritimus Species Name: UrsusArctos

3. SPI 0807.5.3 Variation in Populations Notes  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 …one male …and one female Let call him "Jack" Let call her "Jill"

4. Jack and Jill fell in love one spring and mated. SPI 0807.5.3 Variation in Populations Notes  About 7 months later, Jill gave birth to four male cubs. Jack Dad Mom Jill Shemp Moe Larry Curly Dark Brown Dark Brown Light Tan Light Brown

5. Genes have pairs of alleles which determine physical traits. SPI 0807.5.3 Variation in Populations Notes  • 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. B b 3 cubs will have brown fur B b Bb BB 1 cub will have tan fur (Brown) (Brown) Bb bb (Tan) (Brown) Punnett Square

6. In their local habitat there was a population of 50 bears. • (25 males and 25 females) SPI 0807.5.3 Variation in Populations Notes  • Each mating pair had 4 cubs. • Three cubs were brown, and one cub was tan. • There were 100 cubs born (25 mating pairs x 4 Cubs=100) There were 75 brown cubs There were 25 tan cubs

7. For thousands of years brown fur provided the best camouflage in the Canadian forests. SPI 0807.5.3 Variation in Populations Notes  • 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

8. In the new white environment brown fur was a disadvantage. SPI 0807.5.3 Variation in Populations Notes  Instead light colored fur became an advantage. Many of the brown fur bears died. From Brown Bear to White Bear: The Origin of Polar Bears 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.. Light Tan Fur Brown Fur

9. The lightest color bears had a significant survival advantage. SPI 0807.5.3 Variation in Populations Notes  Over time white colored fur became the norm. From Brown Bear to White Bear: The Origin of Polar Bears