1. Seminar of Botany
Name : Prem Gajanan Nagrale
Class : M.Sc. Part l (Botany)
Semester : ll
Topic : Genetic Drift.
Session 2022 - 23.
Shri. Shivaji College of Arts, Commerce and
Science Akola.
2. Contents :
• Concept of Genetic drift.
• Terminologies.
• Genetic drift vs Natural selection.
• Types of Genetic drift.
• Genetic drift vs Gene flow.
• References.
3. Genetic drift.
Definition : Genetic drift is an evolutionary change in allelic
frequencies of a population as a matter of chance.
1 ) It is basic mechanism of evolution.
2 ) It is independent of selection.
3 ) It is common in small population, no significance in larger populations.
4 ) some allele become dominant while other become less common over a
period of time or may be lost.
5 ) When there is only one allele is left for a particular gene pool that allele is
said to be fixed.
4. Genetic drift vs Natural selection.
• Random process.
• Non direction.
• Non adaptive evolution.
• Loss of genetic
variations.
• Operate on neutral
allele.
• Important allele may
disappear.
• Non random process.
• Directional.
• Occur due to
environmental
challenges.
• Operate by any allele.
• Increase genetic
variations.
• Ends up with survival of
fittest.
6. Founders effect.
Founders effect occurs when portion of population separate from old
population to start a new population with different allele frequency.
1. The new population formed does not interact and mate with the original population.
2. As a result, the allelic frequencies of the new population will be different from the original
population.
3. There are many species that are found only on a particular island.
4. This is due to the founder effect.
5. Their alleles will be responsible for the diversity on that island.
6. These alleles will dominate, and mutations in the population will lead to the formation of
new species.
7. The new population will diverge to such an extent that they will no longer interbreed.
7. Example of Founders effect.
• Silvereyes colonised South Island of New Zealand
from Tasmania in 1930.
8. Bottleneck effect.
In the bottleneck effect, occurs when a natural disaster or similar event
randomly kills a large portion of population leaving survivors that have
allele frequencies that were very different from previous population.
1. The frequency of certain alleles in a population changes because the
organisms that carry them are eliminated.
2. The others increase in number because they are the only alleles left.
3. This is observed during natural disasters like volcanic eruptions,
earthquakes, etc., leading to the death of most of the population.
9. Example of Bottleneck effect.
• Northern elephant seals.
• Bottleneck event : Human hunting (1890).
• Population size 20 at the end of 19th century.
• Now population is 30,000.
• But their genes still carry the marks of this
bottleneck .
• Much less genetic variations.
10. Role of Genetic drift in evolution.
• It affect the genetic makeup of the population.
• Play an important role in evolution of new species.
• Decrease genetic diversity.
• New population genetically district from its original
population.
• Play significant role in allele fixing.
11. Genetic Drift vs Gene Flow :
• Gene flow is the movement of genes between
populations, species, or organisms.
• E.g., bacteria can transfer genes between different
cells.
• On the contrary, genetic drift refers to the random
selection of genes in a population.
• When individuals from one population migrate to
some other population and breed there, gene flow
occurs.
• Unlike genetic drift, gene flow does not evaluate
the allele frequencies.
12. References.
• Population Genetics - A.n. Shukla
• Genetics by Dr. B. D. Singh .
• https://en.m.wikipedia.org › wiki
• https://www.biologydiscussion.com
