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Evolution: Genetic Descent
with Modification
Before we being….
Evolutionary domains
Individuals change, populations evolve
Darwin’s journey and those
Prior to Darwin, Lamarck “Use/Disuse”
1859 published “On the Origin of the
Galapagos Islands-why so critical?
Bio-geographic isolationism
Gives us a way to determine which
species are ancestral and which are
derived in order to determine phylogeny
leading to cladistics.
Phylogeny, the connections between
all groups of organisms as understood
by ancestor/descendant relationships
Cladistics, determining shared, derived
traits to determine ancestry and
evolutionary relationships
5 Key Observations Darwin
1) Organisms have unique traits
2) Traits are inheritable
3) Organisms adapt
4) Nature is cruel-natural selection
5) Differential reproduction (not
everyone produces the same # of
offspring and not all offspring born
How do we get genetic change
from one generation to the next?
Micro-evolutionary process (codical
domain) deals with the biological
processes that change allele frequency.
If there is no change in genes, it is NOT
5 Ways to get allele frequencies to change:
Mutations- missense mutations are point level changes in
the DNA. A single mutation can have a large effect, but in
many cases, evolutionary change is based on the
accumulation of many mutations.
Gene flow is any movement of genes from one population
of like organisms to another. (emigration and immigration)
Sex- which egg and which sperm?
Crossing Over- causes changes in gene sequencing which
can change phenotype.
Genetic Drift – in each generation, some individuals may,
just by chance, leave behind a few more. The genes of the
next generation will be the genes of the “lucky” individuals,
not necessarily the healthier or “better” individuals.
So which changes stick around and which ones don’t??
Whichever traits provide a benefit are selected for by nature
(economic domain).
Natural Selection Is the “chooser”
Natural selection helps determine which
changes stick around. (Remember 5 ways to
get a change).
Natural selection is the nonrandom
process by which traits are selected for by
nature because they provide some survival
If a mutation provides a desirable
phenotype, that phenotype produces a
higher number of surviving offspring. (More
than other phenotypes)
For natural selection to be
able to choose:
There is variation in traits among
There is heredity of those traits.
What is “fitness”?
Fitness is how well adapted, strong, sexy and
capable an organism is based on its genetics.
Those that are at least adequate, in terms
of survival, will leave offspring. If not, no
round two for you!
This is why we maintain variation in any
given species.
Good enough clears the biological bar!
Nature provides a “Normal trait” distribution in
a population, reflecting adequate individuals:
But why can’t we be less than
adequate?? Nature’s cruel!!
Limited resources means that organisms
compete with themselves and others for
survival. Because of this, nature weeds out
inadequate individuals from the group so that
only the most able produce diverse offspring.
The diversity in each generation (descent
with modification) allows each generation to
try and produce “better” offspring in terms of
But even those offspring won’t all live and
The selection process starts early for many
Selection pressures lead to:
A logistic curve (S curve) not or rarely an exponential curve or
J curve.
3 outcomes of natural selection that can be
seen in different populations (Modes of
Directional selection: phenotype of
the group shifts to favor one extreme
over another.
Disruptive selection: both extreme
phenotypes are favored over the middle
Stabilizing selection: the middle
phenotype is favored over the extreme
Three Forms of Natural Selection
Founder Effect and Bottleneck Effect
Founder Effect describes the loss of
genetic fitness of a population when a
few individuals re-colonize a new area
or when only a few survivors are left to
repopulate an area.
Bottleneck Effect (“Bottlenecking”) is
a term to describe a significant loss in
genetic diversity in a population. (Like
from Founder Effect or Genetic Drift)
Remember, even asexual
creatures seek diversity!
Asexual bacteria obtain genetic diversity
through 1 of 3 process; conjugation,
transduction or transformation