Theory of Natural Selection(A)
Popilations grow exponentially and exceed their resources, overpopulation results in a struggle for survival. in every population, variation leads to an unequal chance for survival. only the best fid individuals will survive and reproduce.
Theory of Natural Selection(B)
Some giraffes had long necks and others had short necks. short necked animals could not survive because they could not reach enough leaves to eat. long necked animals survived, until only long necked giraffes were left. no girrafe changed the length of its neck, the population changed.
Types of Natural Selection
Stabilizing selection, Diversifying Selection, Directional Selection, Sexual Selection
Eliminates Extrenes from population, weeds out many mutants. Ex: human babies that are 6-8 pounds have the best survival rate.
Diversifying or Disruptive Selection
Extremes in a population are favored at the expense of intermediate forms.
changing environmental conditions cause one population to replace another. can be very rapid in the following examples: industrial melanism or peppered moths, and antibiotic resistance.
selection based on variation of secondary sexual characteristics. the fittest male gets to mate. elk males have the largest antlers will get to inseminate all the females in a harem.
humans breed plants and animals by seeking desired individuals. humans have bread 3 different planys all from the wild mustard plant
In Preindustrial England most moths were light colored, and then the sooty dark environment gave dark moths the advantage, and they changed majorities quikly
Developing Antibiotic Resistance
bacterial resistance to antibiotics is carried on plasmids that can be transformed from one bacterium to another exposure to a particular antibiotic kills those bacteria not resistant to it, and the rest reproduce in greater numbers than the non-resistant. no individual bacteria becomes resistant, but a change in the population allows them to become more common
Sources of population variation
Tremendous variation is hidden in any gene pool and can be expressed by selective pressures. each of the following leads to a population retaining a great variation of alleles.
the presence of two or more phenotypically distinct forms of a trait in a single population of species