Transcript Gene Frequency and Natural Selection

Gene Frequency and
Natural Selection
Team Brainstormers (BS)
Spring Feb 2015
Relationship between Gene
Frequency and Natural Selection
Gene Frequency
∗ Random genetic
mutations occurs
∗ Inherent Variation
∗ Sexual reproduction
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(According to Hardy-Weinberg, changes ∗
in frequency will not occur in a population
if these five conditions are not met.)
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No mutations
No natural selection
Very large population
Random mating
No gene flow
∗
Natural Selection
Influences from the
surrounding environment
Eliminating incompetent
individuals
Does not produce perfect
organisms
Highly selective and
specific
Natural Selection Methods
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Different populations of prey
Different predators
Adaptation by prey and predators
Different environments
Natural disaster-bottleneck effect
Different rates of survival and
reproduction of prey populations
Gene Frequency Methods
●A starting population of 50 individuals represented by 100 alleles (beads) were picked out of the
cup at random; this essentially signifies random mating.
●Allele pairs were added or removed based on the rate of survival to replicate the introduction of
selective pressures.
●The allele pairs were then counted and beads were added depending on the rate of survival and
reproduction for each case.
●Beads were picked out in pairs at random again, these signify individuals of the second
generation.
●This process was repeated for six generations for all runs except for one case due to a shortage of
beads.
○ That run was carried out until the fourth generation; therefore, all comparative analysis can
only be carried out to the fourth generation and forecasting was used for the subsequent
generations.
●The rates of survival and reproduction for our various runs are greatly exaggerated, with rates
rare- if ever found in nature.
○ The exaggeration is so that we can see the explosive/depressive effects of adaptability, or
lack thereof, to a given environmental condition.
Gene Frequency Results
● According to the graph,
each of the genotype
frequencies remain
constant, therefore
reinforcing the fundamental
points outlined in the Hardy
Weinberg principle.
● This graph entails the
projections of the
genotype frequency
percentages up for
future generations.
Natural Selection Results
First Environment
Population
Size Data
G1
G2
G3
G4
G5
G6
Blue
20
28
40
28
12
13
Light Purple
20
33
40
37
28
40
Orange
20
35
40
40
1
1
Yellow
20
32
40
32
1
0
Green
20
16
20
16
0
0
Pink
20
21
13
16
9
13
Dark Purple
20
29
40
24
9
9
Aqua
0
0
0
0
20
24
Second Environment
●
● The second figure displays the
combined representation of all of
the species
According to the first Figure (Populations with
Projected Decay), the population counts in the
first 6 generations fluctuated, but mainly had
decreased in numbers.
Gene Frequency vs. Natural
Selection
● Selection against one
genotype can result in an
overall positive effect on
others by freeing up
resources such as food and
habitat.
● Fluctuations within subsets
of a population are normal,
overall change in allele
frequency is usually gradual
unless a subset completely
dies out.
Conclusions
★ Natural selection and allele frequency are closely related, if natural
selection is in action, then allele frequencies are changing.
★ The correlation between natural selection and gene frequency can be
modeled in the laboratory using simple non-living systems, in living
systems with much greater complexity, and can probably be modeled using
highly sophisticated computer programs.
★ The allele frequency of the previous generation determines the phenotypic
distribution of the current generation.
★ Natural selection acts upon this generation to refine the positive traits,
weeding out the negative traits due to selective pressures such as
predation, sexual selection, and relative fitness.
★ Therefore natural selection is a direct cause of allele fluctuation within a
population.
References
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Reece, J. (2011). Campbell biology Jane B. Reece ... [et al.]. (9th ed.). Boston: Benjamin
Cummings.
The Paleontological Research Institution and its Museum of the Earth. Types of Natural
Selection.
NY. Paleontological Research Institution. [cited 2015 Feb 19]. Available from
http://bivalves.teacherfriendlyguide.org/
Philip McClean. Evolutionary Genetics [Internet]. Bison (ND): North Dakota State
University; 1997 [updated 1998; cited 2015 Feb 25]. Available from:
http://www.ndsu.edu/pubweb/~mcclean/plsc431/popgen/popgen4.htm
"Modern Theories of Evolution: Hardy-Weinberg Equilibrium Model."Modern Theories of
Evolution: Hardy-Weinberg Equilibrium Model. Available from:
http://anthro.palomar.edu/synthetic/synth_2.htm