A sharp reduction in population size due to environmental or human factors can lead to a founder effect or bottleneck effect. When a new population is established by a small number of individuals from a larger population due to migration or other reasons, it results in increased homozygosity, reduced genetic variation, and decreased heterozygosity in the new population compared to the original population. Both founder effect and bottleneck effect have similar results such as increased similarities between individuals and harmful alleles becoming fixed in the new population.

4. A sharp reduction in size of population due to environmental
events such as femines, earthquake, flood, fire, disease or
drought) or human activity such as genocide
example insect population
More number
(favourable condition)
Less number
(Adverse condition)
Increase number
(favourable condition)

5. Insect B
Insect A
Filling the bottle in
randomly way by
insect
Randomly mix
bottle
Inverted
bottle
Only chance of one type
Black insect population

9. Migration or moment or founder effect when our new population is
established by a very small number of individuals form a larger
population
Migration
Diseased deer 3 Individual
Founder
population
Increase
reproductive
population
Compare
population
Population
Heterozygote New
daughter
population

10. The result of both founder effect and bottleneck effect are
similar
• Maximum homozygotic
• reduce genetic variation
• increase similarities
• decrease heterozygosity
• harmful Alleles may be fixed