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# NATS 1940 Study Guide - Comprehensive Final Exam Guide - Evolution, Natural Selection, Charles Darwin

Department
Natural Science
Course Code
NATS 1940
Professor
Mark Vicari
Study Guide
Final

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NATS 1940

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BIODIVERSITY
October 10, 2017
LECTURE 10
CHAPTER POPULATION GENETICS III: CAUSES OF EVOLUTION
Question 1:
From question frequency of recessive allele is 0.3 =q
Asked to find frequency of recessive trait = q2
0.3X0.3=0.09
Question 2:
Frequency of dominant trait= 84%=0.84= p2+2pq
Therefore, since the total formula equals 1,
Q2=1-0.84=0.16
Q=0.4
P=1-0.4
= 0.6
we need to find heterozygous frequency which is found by 2pq
2(0.4)(0.6)
=0.48=48%
New Definition of Evolution
= a change in the allele and/or genotype frequencies of a population
Collectively, allele and genotype frequencies make up the genetic structure of a
population
Evolution is therefore a change in the genetic structure of a population
A population whose allele and genotype frequencies are constant from one generation
to the next, is not evolving (i.e. it is in H-W equilibrium)
- H-W equation will predict genotype frequencies
Causes of evolution
1. Natural selection
2. Genetic Drift
Natural Selection
Frequency dependent selection
o Occurs when the effect of a trait on fitness (positive or negative) depends on
how common that trait is in the population
i.e., it depends on the frequency of the trait
Perissodus microlepis, a cichlid fish from Africa
o Predator; eats scales off the bodies of other fish
o 2 morphs (physically different types): right-outhed ad
left-outhed
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o Right-mouthed morph attacks from left side
o Left-mouthed morph attacks from right side
More specifically, the cichlid example is an example of negative
frequency dependence
o When effect of a trait on fitness is negatively correlated
with its frequency
o Tends to promote co-existence of different morphs
Positive frequency dependence = When fitness of as morph is
positively correlated with its frequency
o E.g.: many flowers have different color morphs within the
same species
o Some pollinators develop preference for most common
morph in a population --> common morph gets more
visits, becomes more common
Positive frequency-dependent selection is also known as purifying
selection
o Tends to eliminate all morphs except for the one that was
most common to begin with
Discrete Characters
either/or characters with distinct phenotype categories
Variation of this type = qualitative variation
Polymorphism = existence of qualitative variation (i.e., different morphs) in a
population
Quantative Charaters
E.g. height, skin colour, etc.
Continuum of variation
More than one gene involved
Traits for these characters follow a normal distribution ell ure
Width of curve describes the amount of variation in the population
Natural selection can act on quantitative characters in one of three ways ...
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