5.2 Evidence Of Evolution

Topic 5.2
Evidence Of
Evolution
IB DP – CORE

Understandings:
 Natural selection can only occur if there is variation among
members of the same species
 Mutation, meiosis and sexual reproduction cause variation
between individuals in a species
 Adaptations are characteristics that make an individual suited to
its environment and way of life
 Species tend to produce more offspring than the environment
can support
 Individuals that are better adapted tend to survive and produce
more offspring while the less well adapted tend to die or
produce fewer offspring
 Individuals that reproduce pass on characteristics to their
offspring
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02/07/18

 Natural selection increases the frequency of characteristics
that make individuals better adapted and decreases the
frequency of other characteristics leading to changes
within the species.
By Mariam Ohanyan
3
02/07/18
Source: https://creationscience4kids.com/can-natural-selection-make-anything/

The process of natural selection occurs in
response to a number of conditions:
 Inherited Variation – There is genetic variation within a
population which can be inherited
 Competition – There is a struggle for survival (species tend to
produce more offspring than the environment can support)
 Selection – Environmental pressures lead to differential
reproduction within a population
 Adaptations – Individuals with beneficial traits will be more
likely to survive and pass these traits on to their offspring
 Evolution – Over time, there is a change in allele frequency
within the population gene pool
By Mariam Ohanyan
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02/07/18

02/07/18By Mariam Ohanyan
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Source: https://www.slideshare.net/paprescott/evolution-natural-selection2011-10239059

The key components to the process of
natural selection are:
Mnemonic: ICE AGE
Inherited variation/ /ժառանգական փոփոխականություն exists within the
population
Competition/ /մրցակցություն results from an overproduction of offspring
Environmental pressures/ /միջավայրի ազդեցություն lead to differential
reproduction
Adaptations/ /հարմարողականությւոն which benefit survival are selected
for
Genotype frequency/ /գենոտիպի հաճախականություն changes across
generations
Evolution/ /զարգացում occurs within the population
By Mariam Ohanyan
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02/07/18

Mechanisms of genetic
variation
 Meiosis –
Via either crossing
over (prophase I)
or independent
assortment
(metaphase I)
 Sexual reproduction –
The combination of
genetic material from
two distinct sources
creates new gene
combinations in
offspring
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 Mutations –
Changing the
genetic
composition of
gametes

Mutations
By Mariam Ohanyan
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02/07/18
 A gene mutation is a change in the nucleotide sequence of a section
of DNA coding for a specific trait
 New alleles are formed by mutation
Gene mutations can be:
 beneficial,
 detrimental or
 neutral

Detrimental Mutation
Change in the base sequence of a genome that has the effect of
reducing the fitness of the so-affected organism.
Detrimental mutations simply are mutations that negatively impact
an organism's ability to survive and/or reproduce.
By Mariam Ohanyan
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02/07/18
Source: https://raheelsbio11.wordpress.com/page/4/

Helpful mutations
Beneficial mutations can be found throughout the natural world.
Remember, a mutation is a change in your DNA, more specifically, a
mutation that allows your DNA to create a protein that functions
differently than it otherwise would.
Example: In humans, scientists have uncovered a recent mutation in the
receptor proteins of the cell membrane. People possessing this mutation
(though few in number) have shown a resistance to HIV. This is due to the
inability of the virus to bind correctly to the host cell.
By Mariam Ohanyan
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02/07/18

11
Source: http://slideplayer.com/slide/5672344/

Meiosis
By Mariam Ohanyan
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02/07/18
Meiosis promotes variation by creating new gene combinations
via either crossing over or independent assortment
1. Crossing Over
2. Independent Assortment

Crossing over
By Mariam Ohanyan
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02/07/18
Crossing over involves the exchange of segments of DNA between homologous
chromosomes during prophase I
The exchange of genetic material occurs between non-sister chromatids at
points called chiasmata.

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Independent Assortment
The orientation of each bivalent occurs independently, meaning
different combinations of maternal / paternal chromosomes can be
inherited when bivalents separate in anaphase I.

15 Sexual Reproduction
The fusion of two haploid gametes results in the formation of a diploid
zygote. This zygote can then divide by mitosis and differentiate to form
a developing embryo.

Malthusian dilemma
In 1787 economist-philosopher Thomas
Malthus wrote an Essay on Population in
which he described how the environment
limits the size of human populations.
Malthus’s argument is simple:
“Like other animals, human populations
grow exponentially. But food production,
the factor that ultimately limits the size of
the human population, grows linearly.
By Mariam Ohanyan
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02/07/18

Malthusian dilemma
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Adaptations
•Structural: Physical differences in biological structure
(e.g. neck length of a giraffe)
•Behavioral: Differences in patterns of activity (e.g.
opossums feigning death when threatened)
•Physiological: Variations in detection and response
by vital organs (e.g. homeothermy, color perception)
•Biochemical: Differences in molecular composition of
cells and enzyme functions (e.g. blood groups, lactose
tolerance)
•Developmental: Variable changes that occur across
the life span of an organism (senescence/ֆիզիոլոգիական
/)ծերացում

Adaptation
02/07/18
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Source: https://yipjboaconstrictor.wikispaces.com/Modern+Animal-Boa+Constrictor

Changing Allele Frequencies
1

Remember the basic
formulas:
 p2
+ 2pq + q2
= 1 and p + q = 1
 p = frequency of the dominant allele in the population
 q = frequency of the recessive allele in the population
 p2
= percentage of homozygous dominant individuals
 q2
= percentage of homozygous recessive individuals
 2pq = percentage of heterozygous individuals
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PROBLEM #1
 You have sampled a population in which you know that the
percentage of the homozygous recessive genotype (aa) is
36%. Using that 36%, calculate the following:
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1. The frequency of the "aa" genotype.
Answer: 36%, as given in the problem itself.
2. The frequency of the "A" allele.
Answer: If q2
= 0.36, then q = 0.6. Since q = 0.6, and p + q = 1,
then p = 0.4; the frequency of A is by definition equal to p, so the
answer is 40%.
3. The frequencies of the genotypes "AA"
and "Aa."
Answer: The frequency of AA is equal to p2
, and the frequency of Aa is
equal to 2pq. So, using the information above, the frequency of AA is
16% (i.e. p2
is 0.4 x 0.4 = 0.16) and Aa is 48% (2pq = 2 x 0.4 x 0.6 =
0.48).

PROBLEM #2
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Within a population of butterflies, the color brown (B) is dominant over
the color white (b). And, 40% of all butterflies are white. Calculate the
following:
A. The percentage of butterflies in the population that are heterozygous.
B. The frequency of homozygous dominant individuals.

25 Answer
The first thing you'll need to do is obtain p and q.
So, since white is recessive (i.e. bb), and 40% of the butterflies are white, then
bb = q2
= 0.4.
To determine q, which is the frequency of the recessive allele in the
population, simply take the square root of q2
which works out to be 0.632 (i.e.
0.632 x 0.632 = 0.4).
So, q = 0.63.
Since p + q = 1, then p must be 1 - 0.63 = 0.37.
Now then, to answer our questions.
First, what is the percentage of butterflies in the population that are
heterozygous?
Well, that would be 2pq so the answer is 2 (0.37) (0.63) = 0.47.
Second, what is the frequency of homozygous dominant individuals? That
would be p2
or (0.37)2
= 0.14.

Adaptive radiation
 Adaptive radiation describes the rapid evolutionary
diversification of a single ancestral line
 It occurs when members of a single species occupy
a variety of distinct niches with different
environmental conditions
 Consequently, members evolve different
morphological features (adaptations) in response to
the different selection pressures
 An example of adaptive radiation can be seen in the
variety of beak types seen in the finches of the
Galapagos Islands
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Adaptive Radiation
(Darwin’s Finches)
By Mariam Ohanyan
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02/07/18

Adaptive radiation
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https://www.youtube.com/watch?v=iA0NF41tLn8

Evolution of Darwin's finches
 Peter and Rosemary Grant have seen evolution happen over
the course of just two years.
 The Grants study the evolution of Darwin's finches on the
Galapagos Islands. The birds have been named for Darwin, in
part, because he later theorized that the 13 distinct species
were all descendants of a common ancestor. Each species
eats a different type of food and has unique characteristics
developed through evolution.
 For example, the cactus finch has a long beak that reaches
into blossoms, the ground finch has a short beak adapted for
eating seeds buried under the soil, and the tree finch has a
parrot-shaped beak suited for stripping bark to find insects.
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Finches
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Source: https://biosenioritis.weebly.com/1.html

 The Grants have focused their research on the medium
ground finch, Geospiza fortis, on the small island of Daphne
Major.
 Daphne Major serves as an ideal site for research because
the finches have few predators or competitors. (The only
other finch on the island is the cactus finch.) The major
factor influencing survival of the medium ground finch is the
weather, and thus the availability of food. The medium
ground finch has a stubby beak and eats mostly seeds.
 Medium ground finches are variable in size and shape,
which makes them a good subject for a study of evolution.
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Darwin’s finches
 Darwin’s finches demonstrate adaptive radiation and show
marked variation in beak size and shape according to diet
 Finches that feed on seeds possess compact, powerful beaks –
with larger beaks better equipped to crack larger seed cases
 In 1977, an extended drought changed the frequency of larger
beak sizes within the population by natural selection
 Dry conditions result in plants producing larger seeds with
tougher seed casings
 Between 1976 and 1978 there was a change in average beak
depth within the finch population
 Finches with larger beaks were better equipped to feed on the
seeds and thus produced more offspring with larger beaks
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 Medium ground finches with larger beaks could take
advantage of alternate food sources because they
could crack open larger seeds. The smaller-beaked birds
couldn't do this, so they died of starvation
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In 1978 the Grants returned to Daphne Major to document the
effect of the drought on the next generation of medium ground
finches. They measured the offspring and compared their beak size
to that of the previous (pre-drought) generations. They found the
offsprings' beaks to be 3 to 4% larger than their grandparents'. The
Grants had documented natural selection in action.

Antibiotic Resistance in
Bacteria
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An example of antibiotic resistance in bacteria can be seen in the
evolution of Staphylococcus aureus (Golden staph)
Golden staph can cause infections to the skin (lesions and boils) as
well as more serious infections (pneumonia, meningitis)
Historically, these infections were treated using the antibiotic
methicillin
Bacterial strains developed that were resistant to this antibiotic
(methicillin-resistant Staphylococcus aureus – or MRSA)
These strains proliferated while susceptible strains died out (methicillin-
sensitive Staphylococcus aureus – or MSSA)
MRSA infections are now especially present in hospitals and nursing
homes, where the use of methicillin was most common
Medical practitioners now prescribe alternate antibiotic agents to treat
infections caused by Staphylococcus aureus

Antibiotic Resistance in Bacteria
 When treated with antibiotics, the resistant bacteria will
survive and reproduce by binary fission (asexual
reproduction)
 The antibiotic resistant bacteria will flourish in the absence of
competition from other strains of bacteria (killed by
antibiotic)
 Antibiotic resistant bacteria may also confer resistance to
susceptible strains by transferring plasmids via bacterial
conjugation
 The introduction of antibiotic (selection pressure) has caused
the antibiotic resistance gene to become more frequent
(evolution)
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Spread of antibiotic
resistance in bacteria
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NEO DARWINISM
Neo-Darwinism is the synthesis of Darwinian
theory and modern genetics – it combines:
The works of Gregor Mendel in describing how
traits are inherited (Mendelian inheritance).
The works of James Watson and Francis Crick
in elucidating the genetic basis of inheritance
(DNA structure).

Selection pressure/ /Ընտրության ճնշում
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Selection pressures are external agents which affect an organism’s ability
to survive in a given environment
•Selection pressures can be negative (decreases the occurrence of a
trait) or positive (increases the proportion of a trait)
•Selection pressures may not remain constant, leading to changes in
what constitutes a beneficial adaptation
Types of selection pressures include:
•Resource availability – Presence of sufficient food, habitat (shelter /
territory) and mates
•Environmental conditions – Temperature, weather conditions or
geographical access
•Biological factors – Predators and pathogens (diseases)
Selection pressures can be density-dependent (affected by population
size) or density-independent (unaffected by population)

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Source: http://ib.bioninja.com.au/standard-level/topic-5-evolution-and-biodi/52-natural-
selection/selection-pressures.html

Biologists sometimes define two types of
evolution based on scale:
 Macroevolution, which refers to large-scale changes that occur over
extended time periods, such as the formation of new species and
groups.
 Microevolution, which refers to small-scale changes that affect just
one or a few genes and happen in populations over shorter
timescales.
 Microevolution and macroevolution aren’t really two different
processes. They’re the same process – evolution – occurring on
different timescales. Microevolutionary processes occurring over
thousands or millions of years can add up to large-scale changes
that define new species or groups.
By Mariam Ohanyan
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02/07/18

Macroevolution
By Mariam Ohanyan
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02/07/18
Source: http://www.rtgmin.org/2012/06/08/macro-micro-evolution/

Microevolution
By Mariam Ohanyan
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02/07/18
Microevolution refers to varieties within a given type. Change happens
within a group, but the descendant is clearly of the same type as the
ancestor. This might better be called variation, or adaptation, but the
changes are "horizontal" in effect, not "vertical." Such changes might be
accomplished by "natural selection," in which a trait within the present
variety is selected as the best for a given set of conditions, or
accomplished by "artificial selection," such as when dog breeders
produce a new breed of dog.

Microevolution and Macroevolution
 Microevolution describes evolutionary
changes that occur within a short
period of geological time (e.g.
between generations)
 There are three main processes that
promote variation within a population
(biodiversity):
 Gene mutations: A change the
genetic composition of an organism
due to alterations in the DNA base
sequence
 Sexual reproduction: Introduces new
gene combinations in offspring via
random mating and meiotic divisions
 Gene flow: The movement of alleles
into (or out of) a population as a result
of immigration or emigration

 Macroevolution describes
evolutionary changes that occur
over relatively long geological
periods, resulting in speciation
 Macroevolution involves changes
in large populations and often is
associated with significant
environmental change
 Not all populations undergo
constant evolutionary
modifications, some remain
relatively unchanged (stasis)
 When evolutionary changes
prevent two related populations
from interbreeding, then
speciation has occurred.

Artificial Gene Transfer
 The inheritance of particular
characteristics results from the
transmission of associated
genes from one generation to
the next
 As this transmission requires
reproduction by the organism/s
and occurs across generations
it is called vertical gene transfer
 Typically, the only way for most
organisms to develop
particular genetic traits is via
inheriting them from their
parents.
 Bacteria can transfer
genes between
organisms within a
generation via the
exchange of plasmids
by bacterial
conjugation
 This transmission is
called horizontal gene
transfer as it occurs
within a single
generation
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Flashcards
48
1. provide evidence that organisms have
changed over time (evolved)
Answer: Fossils; patterns of early
development; similar body structures:
2. By examining fossils, scientists can infer…
Answer: the structures of ancient organisms.
3. Fossils show how organisms…
Answer : have changed over time
4. Organisms with similar early development
Answer : share common ancestors
Source: https://quizlet.com/86076082/52-evidence-of-evolution-
flash-cards/

Thank you
49

5.2 Evidence Of Evolution

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