Download I. Genetic Equilibrium

Biology, I
Population Genetics and Speciation
NAME: ___________________________________
Date: ______________________
Period: _____
Chapter 16: Population Genetics & Speciation Notes Outline
I. Genetic Equilibrium
A. Traits vary within a population
1. Population Genetics – the study of evolution from a _________________________________.
2. Microevolution – a ___________ - ___________ ____________ in the collective genetic
material (alleles) of a population.

____________evolution – is the occurrence of ___________-scale changes in
gene frequencies, in a population, over a geological time period (i.e., consisting of
_________ ___ ___________evolutions)

Alleles –

Population –
* Individuals do not evlove, populations do.
3. Standard bell curve – Shows that _________ ___________________ have _____________
traits and a ________ individuals have ___________________ traits
4. Causes of variation of traits:

______________________ - random change in a gene

_________________________ - reshuffling of genes in an individual (Meiosis –
crossing over, independent assortment)

______________ ___________________ of gametes – chance union
B. The gene pool – the _______ of ______ the ____________________ in a given population
1. Allele frequency – the number of occurrences of that allele in that populaiton

Determined by dividing ______________________________________________
__________________________________________________________________
in the population.
2. Review of phenotype & genotype

Genotype – the actual ________________ ______________________ (the
combination of alleles for traits.)
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Biology, I
Population Genetics and Speciation
NAME: ___________________________________
Date: ______________________
Period: _____
o _______ Homozygous Dominant
o _______ Heterozygous
o _______ Homozygous Recessive

Phenotype - _____________________________
o Complete Dominance – The above three genotypes, show two phenotypes

Long Bristles (BB and Bb)
3. Predicting phenotype
a. Phenotype frequency – is equal to the _______________________________________
_________________________________________________________ divided by the
___________________________________________________
b. Counting & calculating
(1) Count the alleles of each type in each generation.
Ex. _____R, _____r = a total of _____ alleles in 8 individual in 1st generation
(2) Divide the type of each allele by the total number of alleles.
Ex. _________ = R = ________
AND ___________ = r = ________
Gene Pool Example:
______ individuals in the population (each organism has two alleles per trait), thus
= ______ alleles for trait. If ______ alleles in this populaiton are of the _____ varitey,
and ______ are of the _____ variety, then frequencies of alleles are:

__________ of the genes in the gene pool are _____ - a frequency of ______

__________ of the genes in the gene pool are _____ - a frequency of ______
o Together, _______ + _______ = ________ (all the genes, 100%)
4. Law of Probability – the chances of one gamete having an allele AND meeting with any other
allele is expressed:
frequency of R
x
frequency of R
= frequency of RR pair
x
frequency of f
= frequency of rr pair
Example:
frequency of r
Example:
So that the frequency of Rr = subtracting the the sum of RR + rr from 1.0
Example:
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Biology, I
Population Genetics and Speciation
NAME: ___________________________________
Date: ______________________
Period: _____
C. The Hardy-Weinberg Genetic Equilibrium

Showed frequency of alleles in a population ___________ _________________ for
_________________ IF CERTAIN CONDITIONS ARE FULFILLED.

o In other words, allele frequencies in the gene pool do not change unless acted
upon by certain forces.
Hardy-Weinberg genetic equilibrium – is a ________________________________________
In which ______________________________ and the ______________________ of the
population is ________________.

Five conditions for hypothetical H-W population
1. No net mutations occur (__________________________________________)
2. No Individuals enter or leave the population (____________________ or
_____________________)
3. The population is ________________
4. Individuals must ___________ __________________
5. _____________________________________________________.
**Genetic Equilibrium is a theoretical state. Real populations probably do not meet all these
conditions. Use equation to see causes of DISRUPTION of genetic equilibrium.
II. Disruption of Genetic Equilibrium
Evolution may take place when populations are subject to genetic mutations, gene flow, genetic drift,
nonrandom mating, or natural selection.
A. Mutations: ___________________ in the _______.
B. Gene Flow:
1. Immigration – movement of individuals ___________ the group
2. Emigration – movement of individuals __________ of the group

Both immigration and emigration can affect ___________ _______________________
o Example- males of baboon troops- fight for dominance of group of females.
Females tend to stay in troop born into. Less dominant or younger males move to
a different troop. This ensures gene flow.
B. Genetic Drift:

The phenomenon by which allele frequencies in a population change as a result of
_____________________ _________________ or ________________.

Genetic drift refers to the expected population dynamics of neutral alleles (those defined as
having ______ _________________ or ____________________ ________________ fitness)
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Biology, I
Population Genetics and Speciation

NAME: ___________________________________
Date: ______________________
Period: _____
Natural selection describes the tendency of beneficial alleles to become more common over
time (and detrimental ones less common), genetic drift refers to the tendency of any allele to
vary randomly in frequency over time due to statistical variation alone.
C. Large Populations: ______________ populations tend to ___________________ allele frequencies.
D. Non- random mating (Sexual selection)

Sexual Selection – occurs when certain traits __________________ an individual’s
____________________ at mating.

__________________ are the _________________ ________

o invest more in offspring than males
o many females are unavailable for fertilization (because they are carrying for young or
developing young)
o males tend to be in excess
Sexual selection arises in response to either:
1. _______________ _______________: Intersexual selection, in which females choose
males based upon elaborate ornamentation or male behaviors, or
2. _____________ _________________: Intrasexual selection, in which males compete
for territory or access to females, or areas on mating grounds where displays take
place. Male-male competition can lead to intense battles for access to females where
males use elaborate armaments (e.g., horns of many ungulates).
E. Natural selection: _________ __________________ agents of genetic _______________
1. Stabilizing selection – favors the formation of __________________ __________

______________ _________________
2. Disruptive selection – favors __________________ ___________ rather than average traits

Can ________________ _______ distinct ________________________ from a
single distribution
3. Directional selection – favors the formation of _________-_________________ __________


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A response to a change in the environment can select for traits above or below the
average.
We see a _______________ in the _______________ for the trait (either up or down)
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Biology, I
Population Genetics and Speciation
NAME: ___________________________________
Date: ______________________
Period: _____
III. Formation of Species
A. Definition of species
1. Morphological – a species in a population of organisms that ___________ ___________
(same ____________________ and ____________________)
2. Biological – a speceies in a population of organisms that can successfully interbreed but
cannot breed with other groups
3. Combined – a group of ________________ that ___________ ____________ and can
________________________ ___________________ to create _________________
__________________
B. Isolation & Speciation
1. Geographical Isolation & Allopatric speciation:
•
Results from the ________________________ of population subgroups by
geographic ________________.
•
Geographical Isolation may lead to allopatric speciation (Happens when species
arise as a result of geographical isolation)
2. Reproductive Isolation & Sympatric speciation:
a. Prezygotic isolation – occurs ______________ fertilization
Examples: different sizes-body structure prevents mating, different mating ritual
or behavior, different breeding time, not recognizing songs or calls
b. Postzygotic isolation – occurs _____________ fertilization
Example: embryo does not develop or creates a hybrid organism that is infertile or
weaker
c. Sympatric speciation – reproductive isolation within the ________ geographic ______

________ occur to __________ ___________________ _________________
to organisms that use slightly different niches.
C. Rate of Speciation
1. Gradualism - species undergo ___________ _____________ at a _______________ _______
2. Punctuated Equilibrium – new species arise abruptly

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Differ greatly from their ancestors, and then change little over long periods.
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