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B. Balancing selection of sickle cell trait
1. heterozygotes
-  survival rate against malaria
- about 1 in 5 in African populations at risk for malaria
- about 1 in 100 are homozygous recessive
2. Black populations not at risk of malaria have 
occurrence of the sickle cell allele.
a. no more selection pressure for the trait
b. directional selection away from the sickle cell allele
c. only about 8% of American Black population
d. only 1 in 500 individuals are homozygous
C. Industrial melanism
1. peppered moth (two alleles)
a. light (blends with light tree bark)
b. dark (least prevalent in the population)
2. ratios changed with Industrial Revolution (1850’s)
3. concealment hypothesis
4. Kettlewell experiments
5. demonstrated that allele frequencies are influenced by
environment
6. reversed by pollution cleanup
II. Species Formation
- microevolution: adaptation by a species
- macroevolution: forming new species
- levels of specialization increase to a point where
entirely new species formed
A. Species
1. group of organisms unlike other groups
2. does not integrate extensively with other groups
3. considered the final stage of evolutionary process
B. Ecological races
1. local populations of a species adapt to their environment
2. selections for improvement will occur
3. populations eventually begin to differ
- forming ecological races
4. not yet different species
C. Isolation
1. enhances formation of ecological races and new species
2. there are several isolating mechanisms
- they prevent breeding among newly forming races and species
a. geographic
C. Isolation
1. enhances formation of ecological races and new species
2. there are several isolating mechanisms
- they prevent breeding among newly forming races and species
a. geographic
b. ecological (habitat)
c. behavioral
C. Isolation
1. enhances formation of ecological races and new species
2. there are several isolating mechanisms
- they prevent breeding among newly forming races and species
a. geographic
b. ecological
c. behavioral
d. temporal
C. Isolation
1. enhances formation of ecological races and new species
2. there are several isolating mechanisms
- they prevent breeding among newly forming races and species
a. geographic
b. ecological
c. behavioral
d. temporal
e. mechanical
C. Isolation
1. enhances formation of ecological races and new species
2. there are several isolating mechanisms
- they prevent breeding among newly forming races and species
f. reproductive
- prezygotic mechanisms
C. Isolation
1. enhances formation of ecological races and new species
2. there are several isolating mechanisms
- they prevent breeding among newly forming races and species
f. reproductive
- prezygotic mechanisms
- postzygotic mechanisms
D. Adaptive radiation
1. recent evolution of species from a common ancestor
2. each adapts to a different habitat
3. Darwin’s finches
Timing of Evolution
Gradualism
Punctuated Equilibrium
Which is correct?