mutation, genetic drift and migration

1. MECHANISMS OF
EVOLUTION
MECHANISMS OF
EVOLUTION
MECHANISMS OF
EVOLUTION

2. When certain genes become more or less common in
the population over generations, we refer to this
change as EVOLUTION. Although natural selection is
the mechanism of evolution most commonly
discussed, other evolutionary mechanisms also
change the frequencies of traits (and the genes that
control them) in populations. These include
mutation, genetic drift and migration.

3. P r o c e s s e s o f M I C R O E V O L U T I O N
Genetic equilibrium does not occur in nature because
processes that drive microevolution are always in play:
• Natural Selection
• Mutation
• Genetic drift
• Gene flow
•Recombination

4. N a t u r a l S e l e c t i o n
Natural selection is the mechanism of evolution that explains how
species can become better adapted to their environment. Depending on the
environmental conditions, certain traits may confer an advantage or
disadvantage to the individuals that possess them, relative to others in the
population. If a certain trait confers an advantage, then the individual
possessing the trait may have more offspring than those with other traits. If
the trait is heritable, then the genes that give rise to the trait will be more
common in the next generation. If conditions remain the same, those offspring,
which are carrying the same trait, will also benefit, and pass the genes that
give rise to this trait on to their own offspring. Over time, the advantageous
trait (aka adaptation) will become more common in the population.

5. Natural selection occurs in different patterns depending on species and
selection pressures.
Directional selection- Mode of natural
selection in which phenotypes at one end
of a range of variation are favored. Allele
frequencies shift in a consistent direction
in response to selection pressure
Peppered moth rock pocket mice
Stabilizing selection- Mode of natural
selection in which intermediate
phenotypes are favored and extreme
forms are eliminated
▪ Example: sociable weavers building nests
Disruptive selection- Mode of natural
selection that favors extreme
phenotypes in a range of variation.
Intermediate forms are selected against.
▪ Example: African seed crackers

6. Sexual Selection
Sexual selection is a "special case" of natural selection. Sexual selection
acts on an organism's ability to obtain (often by any means necessary) or
successfully copulate with a mate.
.
Selection makes many organisms go to
extreme lengths for sex: peacocks (top left)
maintain elaborate tails, elephant seals (top
right) fight over territories, fruit flies perform
dances, and some species deliver persuasive
gifts. After all, what female Mormon cricket
(bottom right) could resist the gift of a
juicy sperm-packet? Going to even more
extreme lengths, the male redback spider
(bottom left) literally flings itself into the
jaws of death in order to mate successfully
Sexual selection leads to forms of traits
that enhance reproductive success.
Sexual dimorphism is one outcome
▪ Sexual selection
• Some individuals of a population out
reproduce others because they are
better at securing mates

7. Artificial Selection
Long before Darwin and Wallace, farmers and breeders were using the idea
of selection to cause major changes in the features of their plants and
animals over the course of decades. Farmers and breeders allowed only the
plants and animals with desirable characteristics to reproduce, causing the
evolution of farm stock. This process is called artificial selection because
people (instead of nature) select which organisms get to reproduce.
As shown below, farmers have cultivated numerous popular crops from the
wild mustard, by artificially selecting for certain attributes.
These common vegetables were cultivated from forms of wild mustard. This
is evolution through artificial selection.

8. M u t a t i o n
Mutation is a change in the DNA sequence of the gene. In some
cases a change in the DNA will change the protein produced. The change
in frequency resulting from a mutation in one individual is small, so its effect
on evolution is small unless it interacts with one of the other factors, such
as selection. A mutation may produce an allele that is selected against,
selected for, or selectively neutral. Whether or not a mutation is beneficial or
harmful is determined by whether it helps an organism survive to sexual
maturity and reproduce. It should be noted that mutation is the ultimate
source of genetic variation in all populations—new alleles, and, therefore,
new genetic variations arise through mutation.

9. Mutations are the original source of alleles, but many are lethal or
neutral.
▪ Neutral mutation- A mutation that
has no effect on survival or
reproduction
▪ Lethal mutation- Mutation that
drastically alters phenotype;
usually causes death

10. G e n e t i c D r i f t
Another way the frequencies of certain genes can change is genetic drift
(Figure 1), which is simply the effect of chance. Genetic drift is most
important in small populations. Because the genes in an offspring
generation are a random sample of the genes in the parent generation,
some versions of a gene may not make it into the next generation due to
chance events. If one individual in a population of ten individuals happens
to die before it leaves any offspring to the next generation, all of its
genes—a tenth of the population’s gene pool—will be suddenly lost. In a
population of 100, that 1 individual represents only 1 percent of the
overall gene pool; therefore, it has much less impact on the population’s
genetic structure and is unlikely to remove all copies of even a relatively
rare gene.

11. Figure 1. Genetic drift in a population can lead to the elimination of an allele from a
population by chance. In each generation, a random set of individuals reproduces to
produce the next generation. The frequency of alleles in the next generation is equal to
the frequency of alleles among the individuals reproducing.
ART
CONNECTION

12. Genetic drift can also be magnified by natural or human-caused events,
such as a disaster that randomly kills a large portion of the population,
which is known as the bottleneck effect that results in a large portion of the
gene pool suddenly being wiped out (Figure 2). In one fell swoop, the
genetic structure of the survivors becomes the genetic structure of the entire
population, which may be very different from the pre-disaster population. The
disaster must be one that kills for reasons unrelated to the organism’s traits,
such as a hurricane or lava flow.
Figure 2. A chance event or catastrophe can
reduce the genetic variability within a
population.

13. Another scenario in which populations might experience a strong influence of
genetic drift is if some portion of the population leaves to start a new
population in a new location, or if a population gets divided by a physical
barrier of some kind. In this situation, those individuals are unlikely to be
representative of the entire population which results in the founder effect. The
founder effect occurs when the genetic structure matches that of the new
population’s founding fathers and mothers. The founder effect is believed to
have been a key factor in the genetic history of the Afrikaner population of
Dutch settlers in South Africa, as evidenced by mutations that are common in
Afrikaners but rare in most other populations. This is likely due to a higher-
than-normal proportion of the founding colonists, which were a small sample
of the original population, carrying these mutations. As a result, the
population expresses unusually high incidences of Huntington’s disease (HD)
and Fanconi anemia (FA), a genetic disorder known to cause bone marrow
and congenital abnormalities, and even cancer.

14. ▪ Genetic drift can lead to the loss of genetic diversity (fixation)
▪ Genetic drift- Random change in allele frequencies in a population over time, due
to chance alone
▪ Fixed- Refers to an allele for which all members of a population are homozygous
▪ Genetic drift is pronounced in small or inbreeding populations, such as those that
occur after an evolutionary bottleneck
▪ Bottleneck- Reduction in population size so severe that it reduces genetic diversity
▪ Inbreeding- Non-random mating among close relatives
Genetic Drift and the Founder Effect
▪ A bottleneck can lead to the founder effect
▪ Founder effect- Change in allele frequencies that occurs after a small number of
individuals establish a population
The Founder Effect in Old Order Amish
▪ Populations of Old Order Amish in Pennsylvania are moderately inbred – 1 in 200
is homozygous for the recessive allele that causes Ellis van Creveld syndrome

15. G e n e F l o w
Another important evolutionary force is gene flow (also known as
migration) or the flow of genes in and out of a population resulting from
the migration of individuals or gametes (Figure 3). While some
populations are fairly stable, others experience more flux. Many plants,
for example, send their seeds far and wide, by wind or in the guts of
animals; these seeds may introduce genes common in the source
population to a new population in which they are rare.
Figure 3. Gene flow can occur when an
individual travels from one geographic
location to another and joins a different
population of the species. In the example
shown here, the brown allele is introduced
into the green population.
▪ Gene flow counters the effects of mutation, natural selection, and genetic
drift in a population.
▪ Gene flow- The physical movement of alleles into and out of a population,
as by individuals that immigrate or emigrate

16. Section Summary
 There are four factors that can change the frequencies of genes in a
population.
 Natural selection works by selecting for genes that confer beneficial
traits or behaviors, while selecting against those for deleterious
qualities.
 Mutations introduce new versions of genes into populations.
 Genetic drift stems from the chance occurrence that some
individuals have more offspring than others and results in changes in
gene frequencies that are random in direction.
 When individuals leave or join the population, gene frequencies can
change as a result of gene flow.

17. R e c o m b i n a t i o n
Natural selection is usually the most powerful mechanism or process causing evolution to
occur, however, it only selects among the existing variation already in a population. It does
not create new genetic varieties or new combinations of varieties. One of the sources of
those new combinations of genes is recombination during meiosis. It is responsible for
producing genetic combinations not found in earlier generations.
Sperm and ova are radically different from somatic cells in the number of chromosomes that
they contain. Both male and female sex cells normally get only half of the pair of parent
chromosomes (23 for humans). Which half goes to any one sex cell is a matter of
chance.
Net effect of the meiosis process in terms
of chromosome numbers

18. At conception, a single sperm and an ovum combine their chromosomes to
produce a zygote with the normal full set of 46, but with a new combination of
chromosomes distinct from either parent.
New combinations of existing genes are produced at the beginning of meiosis
when the ends of chromosomes break and reattach, usually on their
homologous chromosome. This crossing-over process results in an unlinking
and recombination of parental genes. In the example below, one end of each
chromosome of this homologous pair is exchanged along with the genes that
they contain. The next generation inherits chromosomes with partially new
sequences of alleles.
Sperm and ovum combining their chromosomes in a new zygote
Crossing-over
The consequence of this recombination is the production of sperm
and ova that can potentially add even greater diversity to a population's
gene pool. However, it does not result in new alleles. Subsequently,
recombination by itself does not cause evolution to occur. Rather, it is a
contributing mechanism that works with natural selection by creating
combinations of genes that nature selects for or against.

19. B a l a n c e d P o l y m o r p h i s m
▪ In balanced polymorphism, non-identical alleles for a trait are maintained
in a population
▪ Balanced polymorphism- Maintenance of two or more alleles for a trait in
some populations. Occurs when environmental conditions favor
heterozygotes over homozygotes
A l l e l e F r e q u e n c i e s
▪ Microevolution (change in allele frequencies) is always occurring in
natural populations
▪ Microevolution - Small-scale change in allele frequencies of a population
or species
▪ Allele frequency- Abundance of a particular allele among members of a
population

20. G e n e t i c E q u i l i b r i u m
▪ Genetic equilibrium- Theoretical state in which a population is
not evolving (allele frequencies do not change)
▪ Only occurs if five conditions are met:
・mutations never occur ・population is infinitely large
・population is isolated from gene flow ・mating is random
・all individuals survive and reproduce equally
P r o c e s s e s o f M i c r o e v o l u t i o n
▪ Genetic equilibrium does not occur in nature because
processes that drive microevolution are always in play:
• Mutation • Natural selection • Genetic drift • Gene flow

21. M a c r o e v o l u t i o n
Macroevolution encompasses the grandest trends and
transformations in evolution, such as the origin of mammals
and the radiation of flowering plants. Macro evolutionary
patterns are generally what we see when we look at the
large-scale history of life.
The basic evolutionary mechanisms — mutation, migration, genetic drift,
and natural selection — can produce major evolutionary change if given
enough time.

22. Six Important Patterns of Macroevolution
• Mass Extinctions
• Adaptive Radiation
• Convergent Evolution
• Coevolution
• Punctuated Equilibrium
• Developmental Gene Changes

23. M A S S E X T I N C T I O N
• Extinction
– Occurs Constantly
– 99% Earths Life Forms Extinct
• Mass Extinctions
– Wipe Out Ecosystems
– Disrupt Energy Flow
– Collapse Food Webs

24. What effects have mass extinctions had on the history of
life? Mass extinctions have:
• provided ecological opportunities for organisms that survived by
making new habitats available
• resulted in rapid evolution that produced many new species
Causes of Extinction:
• habitat loss
• an introduced species
• pollution
• population growth
• overconsumption.

25. A D A P T I V E R A D I A T I O N
Adaptive radiation refers to the adaptation (via genetic mutation) of
an organism which enables it to successfully spread, or radiate, into other
environments. Adaptive radiation leads to speciation and is only used to describe living
organisms. Adaptive radiation can be opportunistic or forced through changes to natural
habitats. It is also known as divergent radiation.
Examples of adaptive radiation are all around us, in every living organism. No
organism today is exactly the same as its original ancestor.
Darwin’s finches are a famous example. The finches are a group of 15 or so bird
species found on the Galápagos Islands. The finches are thought to have evolved from
a single ancestral finch species that arrived on the islands. Over time, each species
has adapted to a specific niche by evolving to have a unique beak shape. The
variation in beak shapes means that every species eats different foods. This allows
them to avoid competing with each other when resources are rare

26. C O N V E R G E N T
E V O L U T I O N
Convergent evolution is when different organisms independently evolve similar traits.
For example, sharks and dolphins look relatively similar despite being entirely
unrelated. Sharks are egg-laying fish with the deadly ability to sniff out blood in the water,
while dolphins are curious mammals that navigate by making clicking sounds and listening for
their echoes. Those differences aren't too surprising, considering that the duo's last common
ancestor swam the seas some 290 million years ago.
From that ancient common ancestor, one lineage struck out on land and evolved into
mammals, including the wolf-like Pakicetus, which would later return to the water and evolve
into whales and dolphins. Another lineage stayed put in the ocean, undergoing tweaks to
become the modern shark. Yet despite their winding paths, both animals ended up in similar
evolutionary niches: streamlined swimmers with smooth skin and water-slicing fins ideal for
chasing down prey.

27. C O E V O L U T I O N
Coevolution is commonly defined as
reciprocal evolutionary changes
brought about by interactions
between species, implying that
interacting species impose selection
on each other.
Coevolution is a complex process that occurs on
many levels. It may appear in situations where one
species interacts closely with several others, such as
the interaction between European cuckoos (Cuculus
canorus) and the other species whose nests they
parasitize; it may involve many species, as in
relationships between fruit-bearing plants and birds; or
it may take place in some subgroups of species but
not others. It is important to note that human
activities often disrupt the process of coevolution by
changing the nature and the extent of the interactions
between coevolving species. Some examples of
harmful human activities include habitat fragmentation,
increased hunting pressure, favoritism of one species
over another, and the introduction of exotic
species into ecosystems that are ill-equipped to
handle them.

28. P U N C T U A T E D
E Q U I L I B R I U M
Punctuated equilibrium is the idea that evolution
occurs in spurts instead of following the slow, but
steady path that Darwin suggested.
Punctuated equilibrium is an important but often-
misinterpreted model of how evolutionary change
happens. Punctuated equilibrium does not:
• Suggest that Darwin's theory of evolution by
natural selection is wrong.
• Mean that the central conclusion of evolutionary
theory, that life is old and organisms share a
common ancestor, no longer holds.
• Negate previous work on how evolution by
natural selection works.
• Imply that evolution only happens in rapid bursts.
The concept of punctuated
equilibrium was, to some, a
radical new idea when it was
first proposed by Stephen Jay
Gould and Niles Eldredge in
1972. Now it is widely
recognized as a useful model for
one kind of evolutionary change.

29. GRADUALISM vs
PUNCTUATED EQUILIBRIUM
Darwin felt that biological
change was slow and
steady, an idea known as
gradualism.
Punctuated equilibrium is a pattern
of evolution in which long stable
periods are interrupted by brief
periods of more rapid change.

30. D E V E L O P M E N T A L
G E N E C H A N G E S
Small Changes In Timing of Genetic Control During Embryonic
Development, Make Big Changes In The Resulting Organism

32. Summary for macroevolution:
 Macroevolution - the origin of eukaryotic life forms; the origin of humans;
the origin of eukaryotic cells; and extinction of the dinosaurs.
 Mass Extinctions - dinosaurs
 Adaptive Radiation - species evolved into several different forms that live in
different ways
 Convergent Evolution - unrelated organisms come to resemble one another
process by which two species evolve in response to changes in each other
over time
 Punctuated Equilibrium - patterns of long, stable periods interrupted by brief
periods of more rapid change
 Gradualism - patterns of slow, gradual change
 Development Gene Changes - are those genes that are critical for pattern
formation and cell fate specification during the development of multicellular
organisms

33. https://www.slideshare.net/PaulVMcDowell/mechanisms-
of-evolution-population-selection-and-change
https://www.youtube.com/watch?v=cuS_WWlfpiY
For more knowledge:

34. References:
https://www.google.com/url?sa=i&url=https%3A%2F%2Fedu.glogster.com%2Fglog%2Fmutations%2F25awgm722ow%3F%3Dglogpedia-
source&psig=AOvVaw0H0ONeLqoL1C_MRBXbiZ9N&ust=1617841795010000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCIjjvMLw6u8CFQAAAAAdAAAAABAD
https://www.google.com/url?sa=i&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FLethal_allele&psig=AOvVaw1_gWzvQaycMGCaOXgDjkvs&ust=1617841460568000&source=imag
es&cd=vfe&ved=0CAIQjRxqFwoTCKjQwOLw6u8CFQAAAAAdAAAAABAD
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.pinterest.com%2Fpin%2F255297872609333314%2F&psig=AOvVaw2w1XAcG38tKACdgQcO95gF&ust=161785218244900
0&source=images&cd=vfe&ved=0CAIQjRxqFwoTCMCRhr6X6-8CFQAAAAAdAAAAABAD
https://i.ytimg.com/vi/HPdLqL_Tzso/maxresdefault.jpg
https://www.google.com/url?sa=i&url=https%3A%2F%2Fslideplayer.com%2Fslide%2F13095330%2F&psig=AOvVaw28PxylnrnK7Wl1sznwkc_b&ust=1617851818079000&source=image
s&cd=vfe&ved=0CAIQjRxqFwoTCIjK4s6X6-8CFQAAAAAdAAAAABAY
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.biologycorner.com%2F2016%2F11%2F06%2Fevolution-and-the-rock-pocket-
mouse%2F&psig=AOvVaw2QHgp60vYymZ0hBj73bCv0&ust=1617851655601000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCJClufKX6-8CFQAAAAAdAAAAABAD
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.the-scientist.com%2Fthe-nutshell%2Fgene-behind-black-peppered-moths-color-change-identified-
33412&psig=AOvVaw1k2ajIZnwpXc2cA2UeRqiG&ust=1617851534674000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCLiZqbiY6-8CFQAAAAAdAAAAABAD
https://evolution.berkeley.edu/evolibrary/article/evo_21#:~:text=en%20Espa%C3%B1ol%20print-,Gene%20flow,to%20new%20cities%20or%20countries.
https://evolution.berkeley.edu/evolibrary/article/evo_48#:~:text=Macroevolution%20refers%20to%20evolution%20of,the%20radiation%20of%20flowering%20plants.
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.pinterest.com%2Fpin%2F587367976392019719%2F&psig=AOvVaw3N0WX8mqOUV1DjSFMQqGlI&ust=16178553982730
00&source=images&cd=vfe&ved=0CAIQjRxqFwoTCJjD6pWj6-8CFQAAAAAdAAAAABAD
https://biologydictionary.net/adaptive-radiation/
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.britannica.com%2Fscience%2Fadaptive-radiation&psig=AOvVaw25nQ1AWLT8-
QiUfiR5MZOf&ust=1617861974617000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCPi959a76-8CFQAAAAAdAAAAABAZ
https://www.expii.com/t/adaptive-radiation-definition-examples-10961
https://www.livescience.com/convergent-evolution.html
https://www.britannica.com/science/mutation-theory
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.expii.com%2Ft%2Fcoevolution-definition-examples-
10963&psig=AOvVaw1127IKiq5qCns2_h9BOmjA&ust=1617863990657000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCMiDy5jD6-8CFQAAAAAdAAAAABAK
https://evolution.berkeley.edu/evolibrary/article/side_0_0/punctuated_01
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.thinglink.com%2Fscene%2F786016337141956610&psig=AOvVaw0tbFLTzY2xFUkCqA_sI5zI&ust=1617864972493000&so
urce=images&cd=vfe&ved=0CAIQjRxqFwoTCKCb8_vN6-8CFQAAAAAdAAAAABAD