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Evolution Part 2
Vocabulary
Adaptive value– the value to the population of an adaptation
Common Descent – organisms have a common ancestor
Struggle for existence – every organism struggles to survive, but only the fittest survive
Genetic equilibrium – situation in which allele frequencies remain constant
Reproductive isolation – organisms become unable to breed and produce fertile offspring
Speciation – a new species is formed
Genetic Drift – random change in allele frequencies that occurs in small populations
Disruptive selection – Form of natural selection where the 2 ends of the distribution curve are favored
Geographic isolation – form of reproductive isolation where 2 populations are separated physically
Behavioral isolation – form of reproductive isolation in which 2 populations have differences in courtship rituals that prevents interbreeding
EVOLUTION Part 2
I. Darwin and DNADarwin did not know how heredity
worked.Two factors he couldn’t explain:
1. Source of variation2. how inheritable traits were passed from one generation to the next
II Gene PoolsCombined genetic information of all the
Members of a particular population.
Two main sources of genetic variation:1. Mutations -- change in sequence of DNA
2. Genetic shuffling – sexual reproduction (crossing-over)
III Genetic Drift
In small populations, an allele becomes more or Less common simply by chance.
IV When will evolution NOT occur?
When there is genetic equilibrium – allele Frequencies remain constant .
* if the allele frequencies do not change , the population will not evolve.
Hardy-Weinburg principle
FIVE conditions to maintain genetic equilibrium:
1. random mating2. large population
3. no movement in or out of population
4. no mutations
5. no natural selection
ORIGIN OF LIFE *Current scientific view of events on early Earth
Primitive Earth
1. Surface- sea of molten rock
2. Atmosphere- gases such as: hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, water NO OXYGEN
3. Earth cooled enough to form crust ; violent volcanic activity
4. More cooling caused thunderstorms which created oceans.
How could organic molecules have evolved under these conditions?
Stanley Miller and Harold Urey simulated conditions on early Earth in the laboratory.
• Filled flask with hydrogen , methane ,ammonia, and water.
• Passed electric sparks through mixture of gases to simulate lightning
• Over a few days, several amino acids began to accumulate (organic compounds)
Sidney Fox demonstrated iteractions
among these organic molecules.
These experiments joined Miller’s
organic compounds into aggregates,
similar in form to “ cell-like ” structures.
These first aggregates were called
heterotrophs and were similar to
prokaryotic bacteria and had the
ability to reproduce.
These discoveries created the heteotroph hypothesis.
Heterotrophs -- anaerobic respiration -- CO2 given off
Autotrophs -- O2 given off – aerobic respiration
Excessive oxygen in the atmosphere produced an ozone layer which gave protection from ultraviolet radiation.
Some anaerobic species became extinct, while others adapted to the environmental change.
PATTERNS of EVOLUTION
1. Punctuated equilibrium• long, stable periods of no change interrupted
by brief periods of more rapid change which produced many new species
2. Gradualismevolution occurs gradually, slowly and continuously
Divergent Speciation