Transcript Ch 04 Origins of Life/ Natural Selection

Ch 04 Origins of Life/
Natural Selection
Ch 04
Section 1
Section 2
Animation: Stanley Miller’s Experiment
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ANIMATION
Origins of Life
First was Formation of the earth’s early crust and atmosphere
Chemical Evolution
(1 billion years)
Small
organic
molecules
form in
the seas
Large
organic
molecules
form in
the seas
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ANIMATION
First
protocells
form in the
seas
Single-cell
prokaryotes
form in
the seas
Biological Evolution
(3.7 billion years)
Single-cell
eukaryotes
form in
the seas
Variety of
multicellular
organisms
form, first
in the seas
and later
on land
How Do We Know Which Organisms
Lived in the Past?
4. Our knowledge about
past life comes from
fossils, chemical
analysis, cores drilled
out of buried ice, and
DNA analysis.
Figure 4-4
B. Natural Selection and Adaptation
1. Evolution is the change in a population’s
genetic makeup over time
a) Populations evolve by becoming genetically
different
b) All species descend from earlier, ancestral
species
2. Microevolution describes the small
genetic changes that occur in a population
over time
3. Sexual reproduction leads to random
recombination of alleles from individual
to individual
Natural Selection
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ANIMATION
Geneor
Flow
or Migration
Gene Flow
Migration
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LINK
4. Over time, a population’s gene pool changes
when mutations in DNA molecules are passed
on to offspring.
a) Mutations are random changes in the
structure/number of DNA molecules in a cell.
b) Mutations occur in two ways.
•
•
Gene DNA is exposed to external agents like X rays,
chemicals (mutagens) or radioactivity.
Random mistakes that occur in coded genetic instructions.
c) Only mutations in reproductive cells are passed to
offspring.
d) Many mutations are neutral, some are deadly; a few
are beneficial.
5. For natural selection to evolve in a
population, three conditions are necessary:
a) The population must have genetic variability.
b) The trait must be heritable, capable of being
passed from one generation to another.
c) The trait must enable individuals with the trait
to produce more offspring than individuals
without the trait; this is differential
reproduction.
6. Adaptations are heritable traits that help
organisms to survive and reproduce better
under prevailing environmental
conditions.
7. Environmental changes require adaptations
also. Organisms must:
a) Adapt to the new conditions.
b) Migrate to an area with more favorable
environment.
c) Organisms that cannot adapt become extinct.
Animation: Moth Populations
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ANIMATION
8. Coevolution is the interactions of species
will cause them to engage in a back and
forth genetic contest in which each gains a
temporary genetic advantage over the
other
a) This often happens between predators and
prey species.
9. Hybridization can occur when individuals off
two distinct species crossbreed to produce fertile
offspring.
a) New species can arise. [ i.e. dog breeds]
10. Horizontal gene transfer is when species (mostly
microorganisms) exchange genes without sexual
reproduction
11. A population’s ability to adapt to new
environmental conditions through natural
selection is limited by its existing genes and how
fast it can reproduce.
a) Humans have a relatively slow generation time
(decades) and output (# of young) versus bacteria
which can reproduce millions in hours!
Horizontal Gene Transfer
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ANIMATION
12. Common myths about evolution through
natural selection.
a) Natural selection can only act on existing
genes and is limited by reproductive capacity.
b) There is no such thing as genetically perfect
organism; the purpose is to leave the most
descendants