DOSSIER: Evolution, NCERT LINE BY LINE

Five factors are known to affect Hardy-Weinberg equilibrium. These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection. When migration of a section of population to another place and population occurs, gene frequencieschange in the original as well as in the new population. New genes/alleles are added to the new population and these are lost from the old population.There would be a gene flow if this gene migration, happens multiple times.If the same change occurs by chance, it is called genetic drift. Sometimesthe change in allele frequency is so different in the new sample of populationthat they become a different species. The original drifted population becomes founders and the effect is called founder effect.

MECHANISMS OF EVOLUTION Although the term “evolution” is often used synonymously with “natural selection,” they are actually referring to different concepts. Evolution is an observable phenomenon in which gene frequencies change over time, but it does not explain why a population is undergoing evolution. This is where natural selection—and other mechanisms—come into play. They explain “the why.” There are four main mechanisms of evolution:
Gene Flow and Genetic Drift: Definitions, Mechanisms, and Outcomes
Header Query/Question Answer/Reply
Definition What is Gene Flow? Gene flow refers to the continuous movement of genes between populations due to repeated migration, leading to changes in allele frequencies in both populations.
Definition What is Genetic Drift? Genetic drift is the random change in allele frequencies within a population due to chance events, often leading to significant genetic shifts over time.
Mechanism How does Gene Flow work? Gene flow occurs through migration and interbreeding between populations, resulting in the exchange and mixing of alleles.
Mechanism How does Genetic Drift work? Genetic drift happens randomly, without deliberate migration, due to unpredictable events like natural disasters or sampling errors, especially in small populations.
Frequency How often does Gene Flow occur? It occurs multiple times and consistently in populations that experience regular migration and gene exchange.
Frequency How often does Genetic Drift occur? Genetic drift is unpredictable and typically occurs in smaller populations where random events can have a larger impact on allele frequencies.
Outcome What happens to genetic diversity in Gene Flow? Homogenization of genetic differences occurs, meaning populations become more genetically similar over time.
Outcome What happens to genetic diversity in Genetic Drift? Genetic drift often leads to divergence, where populations become more genetically distinct, and in some cases, it can even result in speciation.
Homogenization in Gene Flow How does Gene Flow lead to homogenization? – Introduction of New Alleles: Migrants introduce their alleles to new populations.
Example: If Population A has allele X and Population B has allele Y, migration spreads both alleles to each population.
– Equalizing Allele Frequencies: Continuous migration balances allele frequencies between populations, making them more similar.
Example: If allele X is rare in Population B, migration from Population A increases its frequency.
– Reduced Genetic Divergence: Populations that were once genetically distinct become less so.
Example: Two bird populations develop similar feather patterns due to migration.
Homogenization in Gene Flow Does Genetic Drift homogenize populations? No, genetic drift typically increases genetic differences between populations because it occurs randomly and in isolation, often reducing genetic variation within a population.
Examples Can you give an example of Gene Flow? Birds migrate seasonally between two islands, introducing and mixing genetic material repeatedly. Over time, their genetic differences reduce, making the populations more similar.
Examples Can you give an example of Genetic Drift? A storm wipes out a large portion of a small rabbit population, leaving only a few survivors. If those survivors carry unique alleles, those alleles will dominate the gene pool, regardless of their initial frequency.
Genetic Drift, Gene flow , Mutation and Natural Selection Quiz
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