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Science

Learning Intention : 8.LS4.3 Analyze geological, paleontological, and anatomical evidence to support that specific phenotypes within a population can increase the probability of survival of that species. Science. Standards 11 and 12. 8 th Grade. Learning Intention : 8.LS4.4

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Science

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  1. Learning Intention: 8.LS4.3 Analyze geological, paleontological, and anatomical evidence to support that specific phenotypes within a population can increase the probability of survival of that species. Science Standards 11 and 12 8th Grade Learning Intention: 8.LS4.4 Develop a scientific explanation about how natural selection effects the survival of a species in changing environments. Success Criteria I will show that I understand these concepts by earning a high score on the formative assessment (quiz). I Can Statement By the end of this unit I will be able to say... ...I can explain how variations in populations results in species survival.

  2. Phenomenon What phenomenon or phenomena do you see in these pictures? Get in groups. Discuss this, and/or do some online research. Crotalus horridus Crotalus lepidus

  3. Questions for Students to Answers Why and how do these rattlesnakes look so different from each other? how Crotalus horridus Crotalus lepidus

  4. Genetic variation of phenotypes in bears. Question: What phenotypes do you see? From Brown Bear to Polar Bear: The Origin of Polar Bears Species Name: UrsusMaritimus Species Name: UrsusArctos

  5. 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's call him "Jack" Let's call her "Jill"

  6. Jack and Jill fell in love one spring and mated. About 7 months later, Jill gave birth to four male cubs. Jill Jack Mom Dad Shemp Moe Larry Curly Dark Brown Dark Brown Light Tan Light Brown

  7. Genes have pairs of alleles which determine physical traits. 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 light-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 This is variation in this bear population

  8. In their local habitat there was a population of 50 bears. (25 males and 25 females) 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 This is just one example genetic variation in the phenotypes in this population of bears

  9. For thousands of years brown fur provided the best camouflage (structural adaptation) in the Canadian forests. • Yet environments ALWAYS change over time. • Winter started arriving sooner and lasted longer, and the glaciers began to move southward. • It was the start of a new Ice Age

  10. In this changed environment, brown fur was a disadvantage. Light colored fur phenotypes became an advantage. 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 only light colored bears remained because they had better camouflage to blend in while hunting prey. Light Tan Fur Brown Fur

  11. Sometimes, due to the genetic diversity inherent in sexual reproduction, cubs were born whose fur was almost white. These cubs, blended in even better than the light-tan bears. They were better able to hunt prey and thrive. Since the near-white bears were better adapted to the icy/snowy environment, they dominated while the other bears died off.

  12. The lighter colored bears had a significant survival advantage in this new Ice Age environment. Over time lighter colored fur became the norm.

  13. 8.LS4.3 Analyze geological, paleontological, and anatomical evidence to support that specific phenotypes within a population can increase the probability of survival of that species. How did geology effect the survival of bears in this story? What paleontological (fossil) evidence supports the claim that Polar Bears came from Brown Bears? What anatomical differences are there that distinguish Brown Bears from Polar Bears? How did the variation of fur color phenotypes in bears enable them to survive and adapt to the artic conditions? 8.LS4.4 Develop an explanation about how natural selection effects the survival of species in changing environments. How did natural selection effect the survival of Brown bears and help transform them into Polar Bears during the last Ice Age?

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