Evolution Mechanisms and Microevolution

sexual selection

certain traits make an individual more attractive to the opposite sex, and more likely to reproduce

what does sexual selection result in?

• sexual dimorphism, members of the same species having different non-sexual characteristics due to which male the female picks

• traits that handicap the individual, their reproductive chances are increased but it also decreases their ability to survive

Intrasexual Selection

individuals of one sex compete (before or after mating)

• often results in increased aggressiveness and development of male secondary sex characteristics

• increased characteristics in promiscuous species

Intrasexual precopulatory

competing over dominance or specific territories

intrasexual post-zygotic

after the egg was fertilized, induced abortion or infanticide

• a new lion takes over a pride and the females have spontaneous abortion

Intersexual Selection

mate choice, generally the female chooses

• male advertises qualities, female chooses best male

• ex: specific bower bird species build their bowers how the female likes

natural selection works on _________ yet ________ evolve

individuals (same species, same place, same time), species (can breed & produce fertile offspring)

micro evolution

changes in a population’s gene pool from one generation to the next

gene pool

all the genes in the entire population

genetic equilibrium

no changes occur in gene frequency from generation to generation

what causes microevolution?

mutations resulting in new genetic variation

evolutionary mechanisms that alter the existing genetic variation 

mutation

unpredictable change in DNA

• source of new genetic variation 

mutations _______ genetic variation

increase

mutations in ________ are inherited

germ cells

epigenetics

changes in organisms caused by modification of gene expression (what switch is turned on) rather than alteration of the genetic code 

• sequence is the same, but different genes are turned on/off

Genetic Drift 

evolutionary mechanism

• allele frequencies in small populations change by random chance events 

• this event is random, it is not related to reproductive success or better adaptability

genetic drift 

founders effect

small population establish in a new habitat; this new establishing population may not be the same as the ORIGINAL population of where they came from

• random chance that the specific organism ended up in a new habitat

bottle neck effect

result of genetic drift

• drastic population reduction where the original genetic frequencies do not reflect the original genetic frequencies of generations that came before 

what could cause a bottle neck effect?

forest fire where the survivors do not reflect the original genetic frequencies of generations that came before

gene flow

migration of fertile individuals that become introduced to another population with a transfer of gametes from one population to another

gene flow, introducing one population to another 

Natural Selection

evolution mechanisms

a response to the environment- differential reproduction of individuals with different traits depending on how fit they are for the environment

natural selection

for evolution to be natural selection it must be:

heritable variation

differential reproductive success 

the Scarlett honeycreeper south gained a shorter bill after its favorite source of nectar began disappearing and they had to find it else where, what is this an example of?

natural selection - a response to the environment 

natural selection: stabilizing

the “average” trait is selected

natural selection: disruptive

opposites or the extreme characteristics are selected

natural selection: directional

favors one extreme characteristic

directional selection: directing toward one extreme trait

stabilizing selection: favoring an intermediate characteristic

disruptive selection: favoring both extremes

balancing selection

maintains diversity in a population, doesn’t favor one form of a gene over another 

• opposite genes exist equally in a population