Advanced Bio: Microevolution

What are the four mechanisms of microevolution?

- mutation

- natural selection

- genetic drift

- gene flow

What are mutations in microevolution?

random changes in the DNA sequence

How big are the effects of mutations in microevolution?

cannot cause large scale changes alone

How often and where do mutations occur?

relatively rare; occurs most often in somatic cells (mutations not passed on)

What is the definition of Natural Selection?

increases frequency of alleles that enhance survival an reproduction, improving the match between an organism and its environment

What does natural selection lead to?

leads to adaptive evolution

What are the three ways natural selection can occur?

- Directional

- Disruptive

- Stabilizing

What is directional natural selection?

occurs when conditions favor individuals exhibiting one extreme of a phenotypic range; common during environmental change

What is disruptive natural selection?

occurs when conditions favor both extremes of a phenotypic range over individuals with intermediate phenotypes; important in speciation

What is stabilizing natural selection?

acts against both extreme ohenotypes and favors intermediate variants; tend to be reasonable well adapted but less variation

What is genetic drift?

chance events that can cause allele frequencies to fluctuate from one generation to the next

What is the effect of genetic drift?

reduces genetic variation within a population

Where is genetic drift significant?

significant in small populations

Whan can genetic drift cause?

can cause allele frequencies to change at random; can cause harmful alleles to become fixed

What are the two types of genetic drift?

- Bottleneck Effect

- Founder Effect

What is the founder effect?

a few individuals become isolated from a larger population; this smaller group may establish a new population whose gene pool differs from the source

What is an example for genetic drift?

afrikaner population (Huntington's disease); Amish of Eastern Pennsylvania (Ellis-Van Creveld syndrome)

What is the bottleneck effect?

a sudden change in the environment may drastically reduce the size of a population

What is an example for the bottleneck effect?

northern elephant seals, greater prairie chicken

What is gene flow?

transfer of genes into or out of a population due to the movement of fertile individuals or their gametes

What does gene flow do?

can increase variation within a population; tends to reduce genetic differences between populations over time-> reducing speciation