3. Mut at ions
1. mutations:
Is a change in the
sequence of nucleotides
in the DNA
May result in new alleles
or new genes
Is usually harmful
Must be in the gametes
to be passed on to
offspring
4. Mutations are more likely to be
favorable when the environment is
changing
5. Duplicat ions
Duplication mutations can lead
to an expanded genome with
more loci that can take on new
functions
Duplication mutations are
thought to be the reason why
certain mammals have more
genes for detecting odors than
others
6. Mut at ion rat es
Plants and animals
average about 1
mutation for every
100,000 genes per
generation
Mutations happen more
quickly in organisms that
reproduce quickly, like
bacteria
7. 2. Sexual Recombinat ion of
DNA
During crossing over
and fertilization
Produces variations
that make adaptation
possible
Sexual reproduction
results in unique
combinations of genes
every generation
8. Quick Checks
What is “sexual recombination”?
What processes need to occur in cells
for “sexual recombination” to occur?
10. Most evolutionary change the result of…
1. Natural selection
2. Genetic drift
3. Gene flow
Most evolutionary change the result of…
1. Natural selection
2. Genetic drift
3. Gene flow
11. Nat ural Select ion
Results in the
differential
success of
organisms in being
able to reproduce
and pass on their
genes to the next
generation
12. Genet ic Drif t
Fluctuations in allele frequencies in a small
population from one generation to the next
The smaller the size of the population, the more likely
there is to be a major shift in allele frequencies
13. Genet ic Drif t
Evolution by drift is aimless, not
adaptive, because it is chance
alone
Drift is common in two population
events: Genetic bottlenecks and
Founder events.
3 initial breeding
pairs - shift in
gene pool
14. The Bot t leneck Ef f ect
when a population
undergoes a drastic
reduction in size as a
result of chance
events (fire, flood,
drought).
It is completely
arbitrary and
unrelated to
phenotype.
15. The Bot t leneck
Ef f ect
Lack of variation means less
adaptability
Some alleles may be
overrepresented in the
survivors, some
underrepresented, and some
not represented at all.
Humans sometimes create
bottlenecks in other species
16. The
Founder
Ef f ect
a small group of individuals becomes
separated from the larger population. They
may establish a new population with a gene
pool that is not representative of the larger
population. Helps account for the high
frequency of certain disorders in isolated
populations
17. Gene Flow
Gene flow - movement of genes between
populations. Gain or loss of alleles from a
population due to migration of fertile individuals,
or from the transfer of gametes.
Tends to reduce differences between
populations
Gene flow increases the variability of the gene
pool by adding new alleles.
20. Variat ion in a
populat ion
Discrete characters - “either/or”
traits, usually controlled by a single
gene
E.g. - widow’s peak or no widow’s
peak
Phenotypic polymorphism - the
population has 2 or more distinct
morphs for a trait that are fairly
common in the population
21. Genetic polymorphisms - the presence
of 2 or more distinct alleles in the gene
pool of a population
May result in phenotypes that vary
along a continuum, like height in
humans
22. Geographic variat ion
Most species
have geographic
variations in their
gene pools
between different
populations
Due to
environmental
differences
23. Survival of t he
f it t est
Fitness - the contribution an
individual makes to the gene pool
of the next generation for
advantageous adaptations
Relative fitness - the contribution
of a genotype to the next
generation. It is dependent upon
the genetic and environmental
context in which it was expressed
(is it still an advantage to have
that gene?)
24. Modes of Select ion
Directional
Most common during times of change or migration
Favors one end of the phenotype range
25. Modes of Select ion
Disruptive
Occurs when conditions favor the two extremes in
the phenotype range
Most likely to result in speciation
26. Modes of Select ion
Stabilizing -
Favors the average phenotype
Reduces variation in a population
27.
28. Why don’t “negat ive” phenot ypes
event ually disappear ?
Diploids - variation “hides” in
recessive alleles of
heterozygotes
Balancing selection - natural
selection that favors two or
more phenotypes in a
population, called balanced
polymorphism
29. The Het erozygot e
Advant age
When individuals that are
heterozygous for a trait have greater
fitness than homozygotes
Example: sickle cell anemia
AA - normal RBCs but prone to the
worst effects of malaria
aa - have sickle cell anemia
Aa - do not have sickle cell, are
protected against the worst effects of
malaria
30. Frequency Dependent Select ion
The fitness of any one morph declines if
that morph becomes too common in the
population
Common in predator-prey relationships
31. Sexual Select ion
Natural selection for mating success
Sexual dimorphism - the obvious
differences between males & females in
a population
32. Intrasexual selection -
members of the same
sex compete with each
other for mates
Antlers, large size, etc
Intersexual selection -
mate choice -
individuals of one sex
are choosy in selecting
their mate
Peacock tails, etc.
Reflects upon the overall
fitness of the individual
(only healthy males can
grow that big tail)
33. Nat ural Select ion cannot
creat e perf ect organisms
1. New phenotypes are the result of many small
changes to previous phenotypes
2. As the environment changes, previous adaptations
may not be favorable anymore
3. Selection can only act on variations that already
exist in the gene pool
Hinweis der Redaktion
Unique DNA in each individual as a result of sexual reproduction
Crossing over
meiosis