Gene Frequency and Natural Selection

Team Brainstormers (BS)

Spring Feb 2015

Gene Frequency ∗Random genetic

mutations occurs∗Inherent Variation ∗Sexual reproduction

Relationship between Gene Frequency and Natural

SelectionNatural Selection

∗Influences from the surrounding environment

∗Eliminating incompetent individuals

∗Does not produce perfect organisms

∗Highly selective and specific

(According to Hardy-Weinberg, changes in frequency will not occur in a population if these five conditions are not met.)

1. No mutations 2. No natural selection 3. Very large population 4. Random mating5. No gene flow

∗ 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

Natural Selection Methods

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 ResultsFirst Environment

Second 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

● 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.

★ 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.

Conclusions

● 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

References