Genetic drift is a random change in the frequency of genes (alleles) in a population over time, especially in small populations.
It happens by chance, not because one trait is better than another (unlike natural selection).
How It Works
In each generation, only some individuals reproduce.
If, by chance, certain alleles are passed on more often than others, their frequency increases — while others may decrease or disappear.
For example:
If a few plants in a small population produce most of the seeds, the alleles they carry will become more common in the next generation — even if they are not more beneficial.
Types of Genetic Drift
- Bottleneck effect – occurs when a population is suddenly reduced in size (due to a disaster, disease, etc.). The few survivors carry only a small sample of the original genetic diversity.
- Founder effect – occurs when a few individuals start a new population. The new group may have different allele frequencies from the original population.
Contribution to Variation
- Genetic drift changes allele frequencies randomly, creating genetic variation between populations.
- It can lead to loss of genetic diversity within small populations.
- Over time, it can cause populations to evolve differently, contributing to speciation.
In Plants
In small plant populations (like those growing in isolated habitats), genetic drift can change flower color, leaf traits, or resistance characteristics simply by chance.
In short:
Genetic drift is random change in allele frequencies that can increase or decrease variation among populations, especially in small ones.