Natural Selection
SC.912.L.15.13
Describe the conditions
required for natural
selection, including:
overproduction of
offspring, inherited
variation, and the
struggle to survive,
which result in
differential reproductive
success.
What do I need to know?
 the conditions required for natural
selection to occur. These include:
overproduction of offspring, inherited
variation, and the struggle to survive,
which result in differential
reproductive success.
 understand genetic drift and gene
flow.
 how mutation and genetic
recombination increase genetic
variation.
Conditions required for
natural selection
•In any population there is
variation.
•More offspring are produced
than can survive.
•The over production of
offspring causes competition.
•Individuals with the most
advantageous traits
(adaptation) out compete
others, survive and
reproduce.
•This differential reproductive
success causes a change in
the observed phenotypes of a
population.
Source: http://evolution.berkeley.edu/evolibrary/article/evo_14
Conditions required for
natural selection
Guiding Questions
1) How does selection
occur through
differential
reproductive success?
2) What are the two
ways to create
variation in a
population?
3) How do adaptations
lead to the evolution of
a population.
Genetic Drift
•Genetic Drift: Random
change in the number
of times a particular
allele occurs in a
population. Often
occurs in small
populations such as
ones that have gone
through genetic
bottlenecks (drastic
reduction in population
size) or ones that have
colonized a new area
(founder effect).
Source:https://www.lcmrschooldistrict.com/roth/Biology_animate/Ch16/Active
Art/genetic_drift.jpg
Genetic Drift
•Guiding Questions:
What are potential
causes of genetic
drift?
How might genetic
drift impact the
survival of a
population?
Gene Flow
•Gene flow:
Movement of genes
through a large
population or
between members
of different
populations
Source:http://www.mrzimmerman.org/New%20Folder/NEWSTUFF/EvolutionTutoria
l/Geneflow_diagram.gif
Gene Flow
•Guiding Questions:
1) What is gene
flow?
2) What is the
evolutionary
importance of gene
flow?
Causes of Genetic
Variation
•Sexual Reproduction:
Combination of genetics
from two different parents.
Leads to offspring with a
combination of traits from
both parents.
•Genetic Mutation: Changes
in DNA can lead to the
formation of new variants of
a trait.
•Crossing Over: Process in
which homologous pairs of
chromosomes exchanges
pieces of with each other
during meiosis.
Source: http://www.darwinwasright.org/genetics.html
Causes of Genetic
Variation
Guiding Questions:
1) What is genetic
variation?
2) What are the 3
sources of genetic
variation?
3) What is the
evolutionary
significance of
genetic variation?
Show What You Know
 A species that lacks the variation
necessary to adapt to a changing
environment is more likely to
A. develop many mutated cells
B. become extinct over time
C. begin to reproduce sexually
D. develop resistance to diseases
Show What You Know
 Which statement is best supported by
the theory of evolution?
A. Genetic alterations occur every time
cell reproduction occurs.
B. The fossil record provides samples of
every organism that ever lived.
C. Populations that have advantageous
characteristics will increase in
number.
D. Few organisms survive when the
environment remains the same.
Show What You Know
 Science explains that different forms of life
on Earth developed over a long period of
time from a common ancestor. The process
by which unrelated organisms come to
resemble one another (e.g., birds, bats,
and butterflies all having wings) is known
as which term?
A. adaptive radiation
B. convergent evolution
C. genetic drift
D. punctuated equilibrium
Show What You Know
 A particular species of shark normally
reproduces sexually. In captivity, it was
found that a female could also
reproduce asexually. One negative
result from asexual reproduction is
A. increased gene recombination.
B. increased number of males
produced
C. decreased number of eggs used
D. decreased biodiversity within the
species
Show What You Know
 Which concept is best illustrated in the
flowchart below?
A. natural selection
B. genetic manipulation
C. dynamic equilibrium
D. material cycles