Evolution of Populations Chapter 11

Relative (allelic) frequency - the percentage of a particular allele (trait) in a gene pool. Natural Selection- In nature, unequal ability to survive and reproduce Artificial Selection- Mankind “selects” for desired traits I. Genes and Variation

Camouflage- organisms blend-in with surrounding environment Mimicry- species copy another to insure their own survival

gene pool - all the genes that exist within a population I. Genes and Variation

gene flow – movement of alleles into or out of a population

B. Genetic drift - change in allelic frequencies by chance Ex: sudden extinction of a dominant species; small populations most affected

C. Genetic equilibrium - when alleles stay the same from generation to generation The Hardy Weinberg Principle: Allele frequencies will remain constant under five conditions 1.Random Mating 2.Large Population 3.No movement (immigration or emigration) 4.No Mutations 5.No Natural Selection: equal change of survival

II. Natural Selection as Genetic Change A. Natural Selection has 3 affects on phenotype distribution 1.Directional Selection- Individuals on one end of a curve are “better fitted” than the middle or other end Peccaries naturally choose to consume those cactus plants with the fewest spines As a result, at flowering time there are more cacti with higher spine numbers; thus, there are more of their alleles going into pollen, eggs, and seeds for the next generation.

Natural Selection has 3 affects on phenotype distribution 2.Stabilizing Selection- Individuals near center of a curve are “better fitted” than both ends Peccaries are consuming the low-spine number plants, and the insects are killing the high-spine-number plants. As these gene combinations are removed from the cactus gene pool, there is less and less variety possible in subsequent generations.

Natural Selection has 3 affects on phenotype distribution 3.Disruptive Selection- Individuals at upper and lower ends are “better fitted” the ones in the middle Years of collecting have left their toll on the roadside cacti. In this environment, it is maladaptive to be good looking and have a reasonable number of spines. Low spine-number plants are not picked because they don't "look right", and high spine-number varieties are left alone because they are too hard to pick. Gradually, the gene pool changes in favor of the two extreme spine number types.

speciation - evolution of a new species III. Process of Speciation Isolating Mechanisms A. Reproductive Isolation: Two populations cannot interbred and produce fertile offspring B. Behavioral Isolation: Two populations capable of breeding but cannot b/c of courtship rituals

C. Geographic Isolation: Two populations are separated by geographic barriers Ex: Rivers, Oceans, Mountains D. Temporal Isolation: Two or more populations reproduce at different times

Geographical IsolationGeographical Isolation _s_4.html _s_4.html Whale EvolutionWhale Evolution 034_05.html 034_05.html

Convergent Evolution Process by which unrelated organisms independently evolve similarities when adapting to similar environments Produces analogous structures

Coevolution Process by which two species evolve in response to changes in each other

Punctuated Equilibrium Pattern of evolution in which long stable periods are interrupted by brief periods of rapid change

Gradualism Pattern of evolution categorized by slow and constant change