Biology 30
Biology 30
Populations Studies
Page 1
Biology 30
Populations Studies
Page 2
Week 8
A population
 Consists of __________________________________ that occupy a particular
area at the same time
The members of a population are more likely to breed with one another than with other
populations of the same species
 Therefore, genes tend to stay in the ____________________ for generation
after generation
The total of all the genes in all the members of a population at one time is called the …
_______________________________________
Evolution
 is the change in the ___________________________…
 in a population's __________________________…
 from ___________________________ to the next.
In order to see how a population evolves, it is helpful to examine the genetics of a
population that does not change from generation to generation
The _____________________________ provides a model of an unchanging gene pool
This law states that the frequencies of alleles in a population's gene pool remain constant
over generations if all other factors remain constant
For a gene pool to be in the Hardy-Weinberg equilibrium, 5 conditions must be met:
1. The population must be _____________. This means that no immigration or
emigration can occur.
2. ______________ mating takes place. There can be no mating preferences
with respect to genotype.
3. There can be no ______________________. A specific gene must not affect
the survival of the offspring.
4. No _________________ of the particular alleles examined can occur.
5. The population must be __________________. This equilibrium is based on
statistical probabilities and random sampling.
Biology 30
Populations Studies
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If all these conditions are met, the frequencies of two alleles (for example A and a) will
remain constant in a population forever
 or until conditions change
The Hardy-Weinberg law points out that sexual reproduction reshuffles genes but does
not by itself cause evolution
The mathematical expression of the Hardy-Weinberg equilibrium is…
where p = frequency of the _______________________
&
q = frequency of the ___________________________
Hardy-Weinberg Law
Example:
 suppose a certain allele A has a frequency of 0.6 in a population
 since the two alleles must add up to 1… then

–
______________________________
the frequency of a is 0.4
Let's see what happens during reproduction
First, let’s arrange the two alleles and their frequencies on a Punnett square
Then, fill in frequencies for the possible offspring
Biology 30
Populations Studies
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The mathematical relationship governing the gene frequencies is…
p2 + 2pq + q2 = 1
AA + 2Aa + aa = ___________________
Since p = __________ and q = ____________, then
HARDY WEINBERG PROBLEMS.
A tutorial on completing questions like these can be found on PowerSchool.
1. What five conditions must be met for the Hardy-Weinberg equilibrium
2. The Hardy-Weinberg principle was first formulated, by both Hardy and
Weinberg, in response to a question raised by students of Mendelian genetics:
Why, if some alleles are dominant and some are recessive, don't the dominant
drive out the recessives? What is the fallacy in the reasoning underlying that
question? How does the Hardy-Weinberg expression answer that question?
3. In a population with two alleles for a particular trait, B and b, the allele frequency
of B is 0.7. What would be the frequency of the three possible genotypes in the
population?
Biology 30
Populations Studies
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4. In a population with two alleles for a particular trait, A, and a, the frequency of a
is 0.355. What is the frequency of the three possible genotypes in the population?
5. Ten percent of the genes for coat colour in a rabbit population are albino (b) while
90 percent code for black coat (B). What percentage of the rabbits are
heterozygous if the Hardy-Weinberg principle holds true?
6. In a population that is in equilibrium, 16% of the individuals show the recessive
phenotype. What is the frequency of the dominant allele in the population? What
proportion of the population is heterozygous for this trait?
7. The proportion of homozygous recessives of a certain trait in a large population is
0.09. Assuming the gene pool is in equilibrium and all genotypes are equally
successful in reproduction, what proportion of heterozygous individuals would
you expect to find in the population?
Biology 30
Populations Studies
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8. How would the following affect the Hardy-Weinberg equilibrium and the
phenotypes in the population: Increased mutation of A to a (assuming A is a
dominant)? Increased mutation of a to A (assuming a is a recessive)?
9. Assume that Rh blood types are controlled by a single pair of alleles. Further,
assume that Rh-neg. individuals (rr) comprise 15% of a stable population of 1000
individuals. Calculate the frequency of the alleles R and r and the expected
genotype distribution.
10. In England the frequency of the i allele of the ABO blood group series is 0.6.
What is the frequency of the I allele (IA and IB combined)? What proportion of the
population has type O blood?
11. Approximately one child in 10,000 is born with the recessive disease PKU
(phenylketonuria). What is the frequency of this allele in the population? What
percent of the population are carriers of this defective gene?
Biology 30
Populations Studies
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12. In a group of 812 individuals, 91% are tasters. The ability to taste PTC paper is
dominant. What are the gene frequencies in this population? What are the
genotype frequencies?
13. Among black Americans, the frequency of sickle cell anemia is about 0.0025.
What is the frequency of heterozygotes? When one black American marries
another, what is the probability that both will be heterozygotes? If both are
heterozygotes, what is the probability that one of their children will have sickle
cell anemia?
14. Two pirates and three Polynesian beauties settled on a previously uninhabited
tropical island. All five of these settlers had brown eyes, but one man carried the
recessive allele for blue eyes. No new vagabonds arrive on the island and no one
leaves this tropical paradise. When the island population reaches 20,000
individuals, approximately how many people would you expect to have blue eyes
if you assume the population to be in Hardy-Weinberg equilibrium?
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
BB = 0.49 ; Bb = 0.42 ; bb = 0.09
AA = 0.416; Aa = 0.458 ; aa = 0.126
BB = 0.81 ; Bb = 0.18 ; bb = 0.01
P = 0.6; Heterozygous = 0.48 [remember that 16% of the population is homozygous
recessive and therefore 0.16 = q2; q = 0.4]
Heterozygous = 0.42 [0.09 is a number referring to individuals and therefore = q2]
a) No longer in equilibrium… p falls and q rises; b) p rises and q falls
r =0.387; R = 0.613; RR = .376; Rr = 0.474; rr = 0.150 [15% refers to individuals,
therefore q2 = 0.15]
I – 0.4; Type O = 0.36
q = 0.0001, Carrier = heterozygous = 2pq = 0.019998 % = 0.02%
9% = q2… q = 0.3; p = 0.7; AA = 0.49; Aa = 0.42; aa = 0.09
[q2 = .0025… q = 0.05; p = 0.95] Aa = 0.095; [chances that both are heterozygotes =
0.095 X 0.095 = 0.009025 X 100] = 0.9025%; 25% chance of having an affected child
p = 0.9; q = 0.1; bb = 0.01 [which means that 1% of the population is blue eyed… if the
population is 20000 people, then…] 200 people will be blue eyed.
Biology 30
Populations Studies
Page 8
More Hardy Weinberg Practice.
1. In a given population of organisms, the dominant allele (p) has a frequency of
0.72 and the recessive allele (q) has a frequency of 0. 28. Use the Hardy
Weinberg formula to determine the genotype frequencies within the population.
2. In Tanzania, 4% of the population is homozygous sickle-cell anemic (ss). From
this data, calculate the proportion of alleles that are s and S. Also calculate the
proportion of the population that is heterozygous.
3. In a population of 200 pigs, 72 of them show the recessive trait.
a. Find the frequencies of the dominant and recessive alleles.
b. Find the percentage of the population that is heterozygous.
c. Calculate the number of pigs in the population that are heterozygous.
Biology 30
Populations Studies
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4. Albinism is caused by an individual receiving 2 recessive alleles (a). Only one
person in 20 000 is an albino. This individual is homozygous recessive.
Obviously there are many carriers in the population with normal pigmentation.
a. How frequently would one of these people be found in the population?
(that is… what is the frequency of the heterozygous condition?)
b. What is the percent chance that your neighbor is heterozygous?
5. Among black Americans, the frequency for sickle cell anemia is about 0.0025.
a. What is the frequency of the dominant and recessive alleles?
b. What is the frequency of heterozygotes.
c. When one black American marries another, what is the probability that
both will be heterozygous?
Biology 30
Populations Studies
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Hardy Weinberg Activity
Year
Black
Grey
Squirrels Squirrels
(B)
(b)
1995
111
603
1996
146
552
1997
122
652
1998
155
536
1999
125
448
2000
106
378
2001
141
419
2002
151
618
2003
163
536
2004
133
489
2005
134
482
2006
172
511
2007
182
602
Total
Gene
Frequency
B (p)
b (q)
% of Genotypes in the
Population
BB (p2)
Bb (2pq)
bb (q2)
1.
Determine the total population size for each year.
2.
Use the Hardy-Weinberg formula to determine the individual gene and
genotype frequencies for each year.
3.
What conclusions can you make about the changes in gene frequencies for this
population?
Biology 30
Populations Studies
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4.
Explain what would happen to gene frequencies over time if in 2008 a
population of predators was able to locate and kill animals with grey fur more
successfully.
5.
Explain what would happen to the gene frequencies over time, if in 2008 and
new disease started to kill off the population of black-furred squirrels.
6.
Explain what would happen to the gene frequencies over time if the genotype
bb suddenly became lethal to any animal that had it?
a.
Would the b gene ever become zero?
7.
Explain what would happen to the B gene over time if the B gene became
lethal to any animal that possessed it.
8.
Explain how the immigration of a new population of the same species into the
study area might affect the gene frequencies over time.
9.
Explain how the emigration of a segment of the population from the study
might affect the gene frequencies.
10.
What factors cause changes in Hardy-Weinberg Equilibrium?
Following completion of these practice questions, submit the week 8 quiz on PowerSchool.
Biology 30
Populations Studies
Page 12
Week 9
Mutations & Evolutionary Change
Mutations violate the conditions for Hardy-Weinberg equilibrium
because one gene changes into another and therefore _____________
___________________________________________.
Review: a _________________ is any inheritable change in the DNA
of an organism
___________________ mutation
- results from non-disjunction, chromosome breakage or
translocation
__________ mutation
- changes in the nucleotides of a DNA molecule
If a population has a stable gene pool and gene frequencies, it is not
evolving.
If the population does not demonstrate Hardy-Weinberg equilibrium
(i.e. its gene frequencies are not stable) it is in __________________
_________________.
Evolutionary Change
_________________________
- a change in the gene pool of a population over successive
generations
Three potential causes of micro-evolution are
- __________________
- __________________
- __________________
- __________________
- __________________
Biology 30
Populations Studies
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Mutation
A new mutation that is transmitted in gametes ___________________
___________________________________ of a population by
substituting one allele for another
A mutation by itself does not have much effect on a large population in
a single generation
If, however, the mutation gives _____________________________
to individuals carrying it, then it will ___________________________
and the population gene pool will change over successive generations
Genetic drift
- ____________________________________________
Random events may bring __________ or ___________________ to
some individuals regardless of their genetic makeup
The resulting change in the gene pool is called _________________.
Genetic drift plays more of a role in ___________ populations than in
large ones
Example:
Flipping a coin 1000 times compared with flipping a coin 10 times
Example: a population of plants consists of only 25 individuals, 16 are
AA, 8 are Aa and 1 is aa. All AA plants are destroyed in a rock slide,
which alters the relative gene frequencies for subsequent populations.
Founder Effect
- Genetic drift that occurs when a _____________________________
_________________________ separate form their original population
and ___________________________________________.
Allele frequencies of the new population will be ______________ than
the original population
- depend on gene pool of the founding population
Biology 30
Populations Studies
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Bottleneck Effect
- A dramatic ____________________________________, resulting in
genetic drift
The frequency of alleles in the remaining members of the population is
very _____________________ from the original population.
Gene flow
The gene pools of most populations of the same species exchange
genes.
- This violates the Hardy-Weinberg condition that populations
must be ______________ to be in equilibrium
Animals may leave one area and contribute their genes to the pool of a
neighbouring population (___________________) or a high wind may
disperse seeds or pollen far beyond the bounds of the local population
Gene flow between populations may ___________________________
and therefore may result in evolution.
Nonrandom Mating
Mates are _____________ based on different characteristics (not just
love the one you’re with)
Sexual Selection
- Chances of ___________________ depend on animal’s traits
(what makes him more desirable to the female)
- Includes ____________________________ and Behavioural
Differences between sexes
Sexual Dimorphism
- Striking _________________________________ between
males and females
Natural Selection
- Environment selects for particular traits that are more ___________
for surviving in that environment
- “________________________”
Biology 30
Populations Studies
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Population Interactions - Definitions:
___________ – Any group of individuals of the same species who live
in the same area at the same time
 Eg. Population of humans in the food court
_____________ – The association of interacting populations that live
in a defined area
 Eg. Population of the classroom and of the tables,
chairs, trays, etc.
________ – An organism’s habitat and role within a community
 Includes all factors needed to survive and the
organism’s interactions with other species
Population Interactions
In any community, individuals of many populations need to live among
each other.
When/how does competition occur?
 Competition occurs whenever two or more organisms attempt
____________________________________

Such as? ________________________
Population Dynamics:
The interactions among individuals – either within the same
population, or from different populations – are the driving force behind
population dynamics.
Population dynamics definition
________________________________________________________
________________________________________________________
Biology 30
Populations Studies
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Population Dynamics
Individuals are always competing for resources in order to survive.
Hence, there are two basic categories of competition
1. Intraspecific competition
Intraspecific competition = Competition for limited resources
among members of the ________________
SURVIVAL OF THE FITTEST among members of the same species aka
NATURAL SELECTION
Eg. Seeds - Only a few seeds will be able to compete
successfully to obtain what they need of the limited available
resources
Intraspecific competition is very ___________ since the members of a
________________________________________
2. Interspecific Competition
Interspecific competition – Competition for limited resources
between members of different species in the
___________________
Eg. Tree competing with a shrub for light and growing
space
Recall- A niche is___________________________________________
Due to interspecific competition, no two organisms can share the exact
same ecological niche
Interspecific Competition
 If no two species can share the exact same ecological
niche – then why is there interspecific competition?

Biology 30
Interspecific competition occurs when individuals of two
different species are competing for resources within
_________________
Populations Studies
Page 17
Gause’s Principle of Competition
The Theory of ______________________
Two species with very similar niches cannot survive together because
they compete so intensely that one species eliminates the other.
Experiment: Gause raised two species of ________________ with
similar food requirements in the same culture.
One species always _________________ the other (the particular
conditions in the culture determined which species survived)
In nature, species can avoid direct competition by:
o _______________________________________
o (e.g. Hawks and owls)

Dividing resources in some other way
o (e.g. Different organisms hunt for insects in
_______________ of coniferous trees)
Producer-Consumer Interactions
Predation
The most obvious population interactions in a community are those in
which a _______________________.
Predators that specialize in eating only one prey species play an
important role in controlling the population size of the prey species
Eg. _________________________________
The terms predator and prey apply not only to animals that eat other
animals, but to any type of _________________________
relationship
Eg. ____________________________
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Populations Studies
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Plant defense mechanisms against herbivores:
 Thorns, Microscopic crystals in their tissues, Spines or hooks
on leaves

Distasteful or harmful chemicals

Some well-known poisons and drugs are secondary
compounds produced by plants such as ___________ and
______________
Active animal defenses against predation
 Fighting, Hiding, Escaping
Four types of passive defense:
I.
__________________________ defense mechanisms
II.
__________________________ coloration
III.
________________________ coloration
IV.
______________ - where one species resembles another
Symbiotic Relationships
Symbiosis = ______________________________________________
1. ______________ - Both species benefit from the association
 Coliform bacteria in the human gut, nitrogen-fixing
bacteria in nodules of legumes, protists in a termite's gut
2. _____________ - One species benefits while the other neither
benefits nor is harmed
 Remora and the shark
3. ____________ - One species, the parasite, benefits at the expense
of the host
 The parasite takes nourishment directly from the tissues of
its host's body
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Populations Studies
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Regulation of Population Size
Factors Affecting Growth of Populations
The growth of a population is suppressed by both:
 _____________ factors - Non living things in the environment


Sunlight, water, soil, air
_____________ factors - Living things in the environment

Humans, trees, fish, bacteria
The combination of these effects is termed
____________________________________
Factors that regulate the growth of populations are described as
density-dependent or density-independent
The combination of __________ (living) and _____________
(nonliving) factors create environmental resistance

I.
Environmental resistance = The combined effects of various
interacting factors that _________________________
Density ________________ Factors - These factors are
intensified as the population increases in size

II.
Eg. Food Availability, Living space, Waste, Disease
Density-_______________ - The occurrence and severity of
these factors are unrelated to population size

Biology 30
Eg. Weather, Climate, Abiotic factors
Populations Studies
Page 20
Growth and Regulation of Populations
Population density = The number of individual organisms in a given
_________ or ________________
Population Density Formula
Dp = N
or
Dp = N
A
V
D = Density
N = number of organism
A= area
V = volume
Examples:
 44 students/100m2 = _____________________

12 gophers/10.0m2 = _____________________

54 minnows/200 mL = ____________________
Why calculate population density? If you know your community size
you can now estimate the ___________________________.
Example:
 School = 1000m2, therefore

4.4 students/m2 x 1000m2 = ____________________
Field = 200m2, therefore

1.2 gophers/m2 x 200m2 = ______________________
Fish tank = 2L = 2000 mL, therefore
0.27 minnows/mL x 2000mL = ____________________
Note -You need to know how a population is ____________________
_______________________ before taking samples to determine the
population size.
Some populations tend to ________ in certain areas, which can affect
the accuracy of your estimation
Population Growth
A population gains individuals by:
 Natality (aka _____________) and Immigration
A population loses individuals by:
 Mortality (aka _____________) and Emigration
The balance between these four factors will determine whether a
population size grows, declines, or remains the same.
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Populations Studies
Page 21
Although this is the formula given to you… we know the factors that
increase and decrease the population.
Therefore:
(ΔN) = (births + immigration) - (deaths + emigration)
Percent Population Growth
Formula – not given on your data sheet but is intuitive…
Change in population:(ΔN) = (births + immigration) - (deaths + emigration)
Therefore, percent growth = Change in population x 100%
Initial population
=> Percent growth =
__[b + i] - [ d + e]_
x 100%
Initial population
To compare populations of the same species that are different
________ or live in different ______________, the change in
population size can be expressed as the rate of change
__________________.
This measurement gives us per capita growth rate
Per Capita Growth Rate Formula:
cgr = ΔN
N
cgr = Per capita growth rate
ΔN = Change in the number of individuals in a population
N = The original number in the population
Why measure per capita growth rate?
 To examine population size as the
__________________________
Factors that Affect Population Growth
Recall that both biotic and abiotic factors limit the growth of a
population
Population size can be limited by:
 How fast and how often a species can reproduce

Biology 30
The ability of a habitat to support the population
Populations Studies
Page 22
Biotic Potential of Populations, Biotic potential = r
Biotic Potential Definition = The _________________ of offspring that
can be produced by a species under ____________________
ie. The capacity of populations for exponential growth
There are six factors which affect biotic potential of a population
1. Age of onset of sexual maturity
• The _____________ that sexual maturation occurs, the
____________ the biotic potential
2. ___________________
• The more females there are, the greater the biotic
potential
3. Estrous cycles
• The ______________ the time between cycles of sexual
receptivity, the ________________ the biotic potential
4. ____________________
• The more readily available mates are in a population, the
greater the biotic potential
5. Litter or clutch size
• The _________ the litter or clutch size, the ___________
the biotic potential
6. Fecundity
• Fecundity = _____________________________________
•
Biology 30
The greater the fecundity of a species the greater the
biotic potential
Populations Studies
Page 23
Population Growth Patterns
Two Types of Curves to know:
1. Exponential Population Growth: J-Curve
This model predicts unlimited population increase under ideal
conditions (usually a closed population) of unlimited resources - and
then a sharp population decline.
There are four phases in this type of growth pattern:
1. __________ phase
2. _____________ phase
3. _____________ phase
4. __________ phase ("____________")
Examples of organisms that exhibit exponential growth include
bacteria, yeast, some insects
Draw a J-curve.
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Populations Studies
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2. Logistic Growth: S-Curve
 More representative of population in nature

This model incorporates the effects of
______________________ and _____________ on the
population growth rate

Natural populations cannot continue to grow
_________________ there is a limit to the number of individuals
that can occupy a habitat
The carrying capacity is the maximum
__________________________ that the environment can support for
a long period of time.
In populations exhibiting logistic growth, an _____________ is
reached near the carrying capacity of the environment
Carrying capacity (symbolized as K) is a property of the environment,
and it varies over space and time with the
___________________________________________________
Draw an S-Curve
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Populations Studies
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r-selected and K-selected Population Strategies
r-selected Populations: Experience periods of _________________
growth
Characteristics of r-selected species:
o _____________ organisms
o Short life time
o Great ___________________________________
o High rate of reproduction = r
o Insects are examples of r-selected populations
K-selected Populations: Stabilize near the carrying capacity of their
environment (K)
Characteristics of K-selected species:
o __________________ size
o Longer generation time
o A lower _________________________
o Young require _____________________
o Examples include large mammals such as deer, bears,
and humans
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Populations Studies
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A Comparison of r-selected (Opportunistic)
and K-selected (Equilibrial) Populations
R-Selection
K-Selection
Variable and/or
unpredictable
Fairly constant and/or predictable
High juvenile mortality
Low juvenile mortality
Life History
Rapid development
Slow development
Reproductive
Capacity
High reproductive capacity
Greater competitive ability
Short, less than one year
Longer, usually more than one
year
Climate
Mortality
Survivorship
Population Size
Level of competition
Age Sexual Maturity
Body Size
Reproductive
Frequency
Offspring
Length of Life
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Populations Studies
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Change in Communities: Succession
Succession - The sequence of ____________ and ______________ of
species in an ecosystem over time
 Communities are defined by the populations in them.

The stage of succession can be determined by
______________________________________ in a community.
Succession:
I. Primary succession

The initial colonization of a barren habitat by
__________________

____________ is produced during this stage
o Eg. Lichen and mosses growing on rocks
II.
Secondary succession

Re-building of an area that once supported many organisms
o Eg. Mount St. Helen’s
Climax Community
 The stage in ecological succession that is _____________ and
___________________

Usually the _________________ in the stages of succession

Produce ________________________ than they use
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Populations Studies
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Type of Community
Pioneer
Populations
Relationship to Sun
Lots of sun required
Shrubs
Seral
Even less than above
Pine trees
Following completion of these notes, complete the practice questions
on PowerSchool, then submit the week 9 quiz on PowerSchool.
Biology 30
Populations Studies
Page 29