IB Biology 2015

1. Essential idea: The diversity of life has evolved and
continues to evolve by natural selection.
5.1 Natural Selection
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2. Understandings
Statement Guidance
5.1.U.1 Natural selection can only occur if there is variation among members
of the same species.
5.1.U.2 Mutation, meiosis and sexual reproduction cause variation between
individuals in a species
5.1.U.3 Adaptations are characteristics that make an individual suited to its
environment and way of life.
5.1.U.4 Species tend to produce more offspring than the environment can
support.
5.1.U.5 Individuals that are better adapted tend to survive and produce more
offspring while the less well adapted tend to die or produce fewer
offspring
5.1. U.6 Individuals that reproduce pass on characteristics to their offspring.
[Students should be clear that characteristics acquired during the
lifetime of an individual are not heritable. The term Lamarckism is not
required.]
5.1 U.7 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.

3. Applications and Skills
Statement Guidance
5.2 A.1 Changes in beaks of finches on Daphne Major.
5.2 A.2 Evolution of antibiotic resistance in bacteria.

4. Mechanism for Evolution
Natural Selection The ultimate goal of any population is that it must
produce the next generation. This is complicated by four basic
characteristics of life:
1. Variation among individuals means they individually have different
ability to obtain resources. Sexual reproduction promotes variation in a
species.
2. Reproduction Individuals that survive and then reproduce transmit these
variations to their offspring.
*The environment is the agent of natural selection determining which species
will survive.
3. Overpopulation Each generation produces more offspring then the
environment can support.
4. Competition with finite resources along with an increase in the population
there is a competition of those resources leading, a survival of the fittest.

5. 5.2 U.1 Natural selection can only occur if there is
variation among members of the same species.
Variation among individuals means they individually have different ability to
obtain resources. Sexual reproduction promotes variation in a species.
http://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Theba_geminata_variability.jpg/1280px-Theba_geminata_variability.jpg

6. 1. Frequency of Genes (Genetic Variation)
• Inheritable differences among
individuals
• Raw material of evolution
• Happens in 3 ways
A. Mutations
B. Recombination
(meiosis)
C. Fertilization
5.2 U.2 Mutation, meiosis and sexual reproduction
cause variation between individuals in a species.
http://media-2.web.britannica.com/eb-media/70/81270-004-3B7A77F2.jpg

7. A. Mutations
• Permanent change in genetic variation
• Only source of new alleles
• Do not arise out of need
• Causes of mutation
– Spontaneous occurrence
– Radiation
– Chemicals
– Transposons
5.2 U.2 Mutation, meiosis and sexual reproduction
cause variation between individuals in a species.
http://www.britannica.com/EBchecked/topic/376514/Merychippus

8. Results of Mutations
• Harmful
Non-adaptive
Eliminated by selection
• Beneficial
Adaptive
Selected and persist
• Neutral
Neither adaptive nor non-
adaptive
May or may not persist in gene
pool
5.2 U.2 Mutation, meiosis and sexual reproduction
cause variation between individuals in a species.
http://4.bp.blogspot.com/--
zKT77cA4Rc/URACaqRE7kI/AAAAAAAAAFI/ZktOQD8BRkY/s1
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9. Example of a gene mutation: phenylketonuria (PKU)
• C to T base-substitution mutation results in wrong amino acid
(similar to sickle-cell mutation)
• Individuals can not metabolize amino acid phenylalanine an
enzyme needed to degrade phenylalanine is not made so it
accumulates in the brain and causes developmental disabilities.
5.2 U.2 Mutation, meiosis and sexual reproduction
cause variation between individuals in a species.

10. Example of a point mutation

11. Example of a chromosomal mutation:
Klinefelter’s syndrome:
• receipt of an extra ‘X’ chromosome by males-> result is
feminization of secondary sex characteristics, sterility and learning
impairment may be present.
• Chromosomal mutations tend to have less evolutionary
significance because they typically cause death or sterility and will
not be passed on.

12. B. Recombination
• Major source of genetic variation
• Two processes
Segregation
Independent assortment
5.2 U.2 Mutation, meiosis and sexual reproduction
cause variation between individuals in a species.

13. C. Fertilization
5.2 U.2 Mutation, meiosis and sexual reproduction
cause variation between individuals in a species.

14. 5.2 U.3 Adaptations are characteristics that make an
individual suited to its environment and way of life.
http://www.gerlachnaturephoto.com/Yellowstone/Bison3791_MASTER_For_Web.jpg
• Where and how an organism lives is
largely due to its specific adaptations
that allow it to survive and reproduce
in a particular area or habitat
• In other words their structure allows
them to function in that environment
• Polar bears are well adapted to life in
the Arctic. They have a large layer of
blubber to keep them warm. They are
strong swimmers, aided by their strong
forearms and layer of blubber for
buoyancy. They have hollow fur to aid
in insulation as well. For plants, cacti
have water storage tissue and spines
(prevent water loss) because of the
infrequent rainfall in the desert.
• Adaptations develop over time
through natural selection

15. 5.2 U.4 Species tend to produce more offspring
than the environment can support.
http://evolutionbyfl.weebly.com/uploads/3/9/7/9/39791607/5832564_orig.jpg
• Populations tend to produce
more offspring than the
environment.
• For example, fish produce
thousands of eggs but only few
make it to adulthood.
• When parents don’t spend a lot
or even any time caring for their
young, they produce many
offspring. This is a reproductive
method used to make sure
some offspring make it to the
next generation.
• Overpopulation and a limited
amount of resources creates
competition within a
population.

16. 5.2 U.5 Individuals that are better adapted tend to survive
and produce more offspring while the less well adapted tend
to die or produce fewer offspring.
• Within a population, there is
genetic variation between the
individuals in the population.
• The organisms with the
beneficial characteristics will be
able to out-compete the other
individuals with the less
beneficial or harmful genetic
traits for limited resources and
mates.
• These individuals will survive
and reproduce and pass these
genetic traits onto the next
generation of offspring.
• Organisms with less desirable
traits will die or produce less
offspring

17. LaMarck
• Organisms adapted to their
environments by acquiring traits
– change in their life time
• Disuse
organisms lost parts because they did not use them — like the
missing eyes & digestive system of the tapeworm
• Perfection with Use & Need
the constant use of an organ leads that organ to increase in size —
like the muscles of a blacksmith or the large ears of a night-flying
bat
– transmit acquired characteristics to next generation
Modern Theory: Mechanism for Evolution
5.2 U.6 Individuals that reproduce pass on characteristics to their offspring.
[Students should be clear that characteristics acquired during the lifetime
of an individual are not heritable. The term Lamarckism is not required.]

18. 5.2 U.6 Individuals that reproduce pass on characteristics to their offspring.
[Students should be clear that characteristics acquired during the lifetime
of an individual are not heritable. The term Lamarckism is not required.]

19. 5.2 U.7 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.

20. Populations evolve
• Natural selection acts on individuals
– differential survival
• “survival of the fittest”
– differential reproductive success
• who bears more offspring
• Populations evolve
– genetic makeup of
population changes
over time
– favorable traits
(greater fitness)
become more common
Presence of lactate dehydrogenase
Mummichog
5.2 U.7 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.

21. Distribution of genes (population genetics)
•is the study of genetic variability in a population
*Extension of Mendelian genetics
•Populations are individuals of the same species that live in
the same locations
Exhibit variation in traits
•Examination of the assemblage of traits reveals genetic
information and shows the kind and proportion of alleles in a
population
5.2 U.7 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.

22. Genes and Populations
• Gene pool: The collection of genes in a population
Because diploids have only two versions of each gene, each has only a
small fraction of possible alleles in a population
• Genotype: The genetic makeup of an individual at a given locus, taking into
account the two possible alleles
Genotype frequencyGenotype frequency is the proportion of a given genotype in the
population
Allele frequencyAllele frequency refers to the proportion of a particular allele, such as A
or a
• Phenotype: the traits of an individual
Phenotype frequencyPhenotype frequency is the proportion of a given phenotype in the
population
Phenotype frequency is influenced by the dominance characteristic of
an allele
5.2 U.7 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.

23. Alleles and Population Genetics
• Although individuals are affected by the process of natural
selection, it is the makeup of the population that is critical for
determining the subsequent generations
• Changes in the gene pool refer to changes in the frequency of
the alleles
• If the allele frequencies in a population do not undergo
change over time, we say that the population is in genetic
equilibrium
5.2 U.7 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.

24. Warbler finch
Woodpecker finch
Small insectivorous
tree finch
Large
insectivorous
tree finch
Vegetarian
tree finch
Cactus finch
Sharp-beaked finch
Small ground
finch
Medium
ground finch
Large
ground finch
Insect eaters
Bud eater
Seed eaters
Cactus
eater
Warbler
finch
Treefinches
Ground
finches
Darwin’s finches
• Differences in beaks
– associated with eating different foods
– survival & reproduction of beneficial adaptations to foods
available on islands
5.2 A.1 Changes in beaks of finches on Daphne Major.

25. Darwin’s finches
• Darwin’s conclusions
– small populations of original South American finches landed
on islands
• variation in beaks enabled individuals to gather food
successfully in the different environments
– over many generations, the populations of finches changed
anatomically & behaviorally
• accumulation of advantageous traits in population
• emergence of different species
5.2 A.1 Changes in beaks of finches on Daphne Major.

26. Darwin’s finches
• Differences in beaks
allowed some finches to…
– successfully compete
– successfully feed
– successfully reproduce
• pass successful
traits onto their
offspring
5.2 A.1 Changes in beaks of finches on Daphne Major.

27. 5.2 A.1 Changes in beaks of finches on Daphne Major.
Changes on the island story
https://whyevolutionistrue.files.wordpress.com/2014/08/05jpessa1-master675.jpg

28. Antibiotic resistance story
http://www.blueplanetgreenliving.com/wp-content/uploads/2009/08/Pill-bottles.jpg
• Antibiotics kill bacteria directly or weaken
the bacteria so your immune system can
fight and destroy the invading pathogen.
• Some bacteria might not die because of
changes within their DNA. These changes
could be caused by mutations within their
genome or the transfer of an antibiotic
resistant gene from another bacterium.
• Resistance is more likely to occur if the
proper amounts of antibiotics aren’t taken
or if a patient doesn’t finish the
prescription.
• These resistant bacteria will survive and
reproduce, creating more identical resistant
bacteria.
• These resistant bacteria will make the
person sick again in the future.
• However if given the same antibiotic, these
bacteria will no longer be destroyed.
• Another antibiotic can be prescribed to kill
these new resistant bacteria.
• Resistance can be passed onto other
pathogenic bacteria, creating more species
of resistant bacteria.
5.2 A.2 Evolution of antibiotic resistance in bacteria.