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