Life Sciences · Ecology · Evolution · Research / Principles and Exploration
Natural selection and genetic drift — principles and investigation
Allele frequencies can vary due to natural selection due to differences in survival and reproduction and genetic drift due to chance in the sample. Changes by generation are compared by changing the environment, group size, initial frequency, fitness, and random number seed. Try to interpret one-time results by distinguishing them from trends in repeated observations.
How does it work?
If neutral, the expected frequency remains the same, but individual trajectories are shaken. In large groups, the relative size of the drift is reduced and trends in selection become easier to read.
p selection=pwA/[pwA+(1−p)wa] → mutation → Binomial(2N,p)/(2N)
Try this investigation
- The scene is the first iteration of the rabbits. The frequency of bright A and dark A is tracked for 50 generations and 5 times. Snow and forest reverse the direction of application of fitness.
- Record the snow environment and neutral environment 5 times each at N=100. The same seed and conditions create the same five trajectories.
- In a neutral environment, change only N to 10·1000 to compare the size of genetic drift, and change only the environment to a forest in the standard condition to see the direction of choice.
Interpreting your results
How do natural selection and genetic drift differ?
Selection is directional due to differences in contribution to survival and reproduction, and drift is a contingency of a finite sample that occurs even with the same probability. The two can work simultaneously.
Assumptions and limitations
It is a Wright-Fisher model of fixed size and random mating without introgression or exodus. In each generation, 2N alleles are restored and extracted. Fitness is a virtual relative value that combines survival and reproduction contributions, and is a multiplication model with genotype fitness AA=wA², Aa=wAwa, and aa=wa². Rabbit color is an intermediate genetic representation of AA light, Aa medium, and AA dark, and the actual fur color inheritance is not predicted. Two-way mutations have the same probability, and linkage, age structure, and actual evolution rate are omitted. The picture summarizes the first iteration with a maximum of 100 animals.