Download Genetic Variation is the Key to Natural Selection

Natural
Selection
Genetic Variation is the Key to
Natural Selection
• Variation is
common among
populations.
• Only genetic
variation has
evolutionary
consequences.
Mutation and Recombination
• Generate variation.
• Mutations are usually
harmless or bad.
• Sometimes they can be
good.
• Recombination (like
crossing over) also
plays a large role in
genetic variation.
Variation is Preserved in a
Population.
• Diploidy – the presence of more than one
allele is often hidden by a dominant allele.
• Occurs even if the gene that is being hidden
is lethal.
• Ex. most genetic disorders are preserved
because of diploidy.
Variation Within a Population
• Polymorphism
– 2 or more
contrasting
forms within a
population
Variation Between Populations
• Geographic
Variation – between
different populations
in different areas.
• Cline – type of
geographic variation
that occurs over a
gradient.
The percentage of the B allele in ABO blood
group.
Genes that are bad now…
…may be good in the future
Balanced Polymorphism – when
genetic diversity is selected for.
• Heterozygote advantage – heterozygotes
show a greater survivorship than
homozygotes
• Example: sickle cell anemia.
Balanced Polymorphism – when
genetic diversity is selected for.
• Hybrid vigor – when 2
inbred varieties are
crossed, the hybrids
show a greater
survivorship and
growth pattern.
• Recessive alleles are
hidden.
Balanced Polymorphism – when
genetic diversity is selected for.
• Frequency dependent
selection – reproductive
success of one morph
declines if that phenotype
becomes too common.
• Example: one insect
mimics a poisonous one.
If the nonpoisonous one is
too common, predator is
less likely to be fooled.
Neutral Variation
• Has no selective pressure.
• Does not influence reproductive success.
• Example: fingerprints
Types of natural selection:
• Directional selection - the population consistently
moves in one direction.
– Changing environmental conditions or new
environment.
• Stabilizing selection – acts against extreme
phenotypes (favors average)
– Most common in stable habitats
• Diversifying Selection – Favors extremes (results
in balance polymorphism)
• Natural selection has no goal, there is no perfect organism.
• Natural selection only works with what we have.
• Organisms do not develop traits in order to fit the
environment. Traits that happen to fit the environment best
allow for more reproduction.
Mechanical Protection
Mechanical Protection
Warning Patterns
Protective Pattern
Cryptic coloration
Deceptive Coloration
Batesian Mimicry
Mullerian Mimicry
• Several unpalatable species share warning
colors or patterns to evade predation.
Predator mimicry
Distraction/Confusion Behavior
Warning Sound
Altruism
Physiological Adaptations
Commensalism
Parasitism
Parasitism