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Transcript
Warmup
Is it more important for a person to be intelligent or fast?
Is it more important for a cheetah to be intelligent or fast?
Be prepared to explain your answer.
1
Warmup
Which came first; the chicken or the egg?
2
NOVEMBER 17TH 2010
Variation and Natural
Selection
3
Variation
Trait: a distinguishing characteristic or quality, esp. of one's personal
nature: bad traits of character.
Attribute: to consider as a quality or characteristic of the person, thing,
group, etc., indicated: He attributed intelligence to his colleagues.
Variation: differences in traits or attributes within the same species.
When we talk about variation, are we seeing differences in the genotype or
the phenotype?
4
Variation Examples
•Finches
•Dogs
•Snails
•Bi-valves
(multiple
species)
5
Traits: Good or Bad
Moths hide so that they don’t get eaten by birds.
Clean trees mean light moths hide well.
After pollution, trees got covered in soot. Now dark moths hide well.
In each scenario, which moth is more likely to survive and have kids?
6
Natural Selection
Environment: all of the space, creatures, and things an organism interacts
with in order to get food, shelter, mates, and safety.
Natural Selection:
•Organisms with helpful traits get food, survive, and have more kids.
•Organisms with harmful traits starve, die, or can’t find mates.
The environment is the context in which the traits are selected for or against.
7
Adaptation
Adaptation: A trait which is helpful in the context of a particular
environment.
Ex: A giraffe’s long neck helps it reach leaves higher off the ground than its
competition.
Ex: The turtle’s instinct to bury eggs in the sand helps more offspring
escape predation than leaving them on the beach.
8
Variation and Natural Selection
Example 1
A garden has red, white, and pink flowers.
What is the variation?
The gardener only likes red ones, so he weeds the others.
What is the selection against?
As a result of selection, what will the next generations of flowers tend to be?
Which trait is becoming more common?
Which trait is becoming less common?
What is happening from the perspective of the genes of the parents?
9
Variation and Natural Selection
Example 2
The allele L stands for long legs, and l stands for short legs on gazelles.
Fast gazelles escape from lions, survive, and get to have kids.
After many generations, which allele will be left in the gene pool, and which
one will be nearly gone?’
Use the vocabulary variation, environment, selected for, selected against in
your answer.
10
Variation and Natural Selection
Example 3
Birds with a heavy-duty beak can crack nuts open to get extra food, but
they also fly slightly slower when running from hawks.
Describe the interaction between the environment and the trait.
Under what circumstances might a heavy-beaked bird thrive?
11
Variation and Natural Selection
Example 4
A population of mice have exclusively dark fur. They do well living in a dark
forest, but a nearby white sand dune blows in and covers up the forest.
There’s still a source of food for the mice, and plenty of predators.
What will happen?
Under what circumstances could the mice thrive?
If thousands of forests get covered up and re-grow over the course of
billions of years, is it likely that in one of these situations a beneficial
mutation could occur to create a new allele?
12
Goals
Students will be able to describe how variation and natural selection can cause
adaptation.
Students will be able to describe how speciation, genetic inheritence, and
branching tree diagrams relate to evolution.
Students will be able to describe and explain evidence for the theory of evolution
in the form of:
•Homologous structures
•Vestigial structures
•Analogous structures
•Embryology
•Branching diagrams with DNA evidence
•Fossil record
•Computer modeling
•Real modeling
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