Genetic Drift: Understanding the Random Process of Allele Frequency Changes, Summaries of Genetics

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Genetic Drift

Organic Evolution

Genetic Drift - Objectives

• Understand the importance of genetic drift as an

evolutionary mechanism

• Identify the main characteristics and

expectations of evolution under genetic drift

• Explore the effects of population size, physical

barriers, and mutation rate on a population

evolving under genetic drift

Genetic Drift - Theory

❖ What is genetic drift?

The chance changes in allele frequency that

results from the random sampling of gametes

from generation to generation in a finite

population

Overview of today’s activity

• Introduction to genetic drift simulation
• Follow along with your TA to learn how the

simulation works and features of genetic drift

• Explore variations in simulations of genetic drift

with your neighbor

• Summarize conclusions

Genetic Drift - Simulations

1. Population

composed of

haploid

individuals

• Each square

is a haploid

individual

• Each color

represents

an allele

2. Here we can

see the change in

the number of

alleles in the

population

through time

3. Here we can

see the change in

allele frequency

through time

4. Here we can modify the

mutation rate ( e.g. set to zero)

Simulation components:

Genetic Drift - Simulations

Each allele (color) has a

probability of being

passed on to zero, one,

or more neighboring

squares after each non-

overlapping generation

How does the simulation

work?

Genetic Drift - Simulations

• What happens to the number

of alleles after several

generations?

• How many distinct alleles

exist in the population after

several generations?

• What are the allele

frequencies after several

generation?

• What is the probability that

any allele will go to fixation

(freq. = 1) or extinction?

• What do we expect to happen when we introduce a

barrier?

• Which allele will fix in each of the four populations?

Would it be the same allele or a different one?

Genetic Drift - Barriers

• What happened to the

allele frequencies?

• What happened to the

variability within each

population (block)?

• What happened to the

variability between

populations (blocks)?

Genetic Drift - Barriers

Genetic Drift – Open barriers

What would happen if we

don’t introduce a complete

barrier from the start?

What would happen if we

open one of the barriers?

As a group, explore the different outcomes of genetic drift

following these discussion questions:

Genetic Drift – Exploration

http://cartwrig.ht/apps/genie/ Go to the following link:

A. What would happen if the boundaries are not of the same size?

e.g. smaller vs. larger population

B. What happens in corridors?

C. What happens when a barrier is removed after a number of

generations?

D. What happens when an incomplete barrier is created (passage)?

E. What happens when we open a passage? What if we do it after

20 generations? What about 120 generations?

F. What happens if we modify the mutation rate? e.g. increasing vs.

decreasing