EVOLUTION
Artificial and Natural Selection
Natural Variation
Darwin observed that there is ______variation among ______.
He also believed that because ______organisms were born than could possibly ______, the struggle for survival kept Earth from being ______by plants and animals.
Natural selection is ______
______
In ______, the environmental conditions choose the ______that are most beneficial, so that only those organisms with the ______traits are reproducing.
Selective Breeding
Darwin noticed that when ______and ______choose which animals or plants to mate they are relying on the fact that there are ______traits in the population
No two individuals are exactly ______, and variation is ______, meaning it can be passed on to future generations
Artificial Selection
Farmers chose ______characteristics
______provided variation, humans controlled the ______
This is called ______
Has resulted in a wide range of ______and ______that are very different from their ______
Selection in Nature
Inheritable variation exists in ______as well
Because each organism is slightly ______, each has slightly different ______and ______
Some individuals are more______than others (better suited to survive and ______, or survival of the fittest)
Generation after generation, the struggle for existence selects the ______individuals to ______and reproduce
Species in general become better ______to their environments as they respond to selection ______
Where does variation come from?
Variations in ______are variations in ______
Traits are controlled by ______
Inheritable variation comes from ______in genes (______)
Differences in genes come from ______and ______
Mutations and Variation
Mutation rates vary by ______
–Humans have a ______rate, bacteria have a ______rate
Can be ______or ______
Gene Shuffling and Variation
Sexual reproduction is an important source of variation in nature
Genes are shuffled during meiosis when gametes are formed
Even the same genes combined in different ways produce different results
Principles of Natural Selection
Individuals in a population show variations among others of the same species.
Variations are inherited.
Animals have more young than can survive on available resources.
Variations that increase reproductive success will be more common in the next generation.
Inheritable Variation
Variation occurs at all levels (physical and biochemical)
Many traits are also polygenic, creating a range of phenotypes
Natural selection does not act on genotype –affects variations in phenotype only!