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Hardy Weinberg’s Principle

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Hardy- Weinberg Principle:  

  • In a given population one can find out the frequency of occurrence of alleles of a gene or a locus.  
  • This frequency is supposed to remain fixed and even remain the same through generations. 
  • Hardy-Weinberg's principle stated it using algebraic equations. 
  • According to this principle, allele frequencies in a population are stable and constant from generation to generation. 
  • The gene pool (total genes and their alleles in a population) remains constant. This is called genetic equilibrium.
  • Sum total of all the allelic frequencies is 1.
  • E.g., Consider, in a diploid, p and q are the frequencies of alleles A and a respectively. 
  • Frequency of AA= p2 
  • Frequency of aa = q2 
  • Frequency of Aa = 2pq 
  • Hence p+  2pq + q= 1 [binomial expansion of (p+ q)2] 
  • Change of frequency of alleles in a population disturbs Hardy- Weinberg equilibrium. This change is due to evolution. 

Factors affecting Hardy- Weinberg equilibrium: 

  • Gene migration: Gene flow from one population to another. Here gene frequencies change in both populations. Gene flow occurs if migration happens multiple times. 
  • Genetic drift: The gene flow by chance causes a change in frequency. Sometimes the change in frequency is so different in the new sample of the population that they become a different species. The original drift effect becomes the founder which is called the founder effect. 
  • Mutation: It results in the formation of new phenotypes. Over a few generations, these lead to speciation.
  • Genetic recombination: Reshuffling of gene combinations during crossing over resulting in genetic variation.
  • Natural selection: It is 3 types. 
  1. Stabilizing selection: Here, more individuals acquire mean character value, and variation is reduced. 
  2. Directional selection: Individuals of one extreme (value other than mean character value) are more favoured. 
  3. Disruptive selection: Individuals of both extremes (peripheral character value at both ends of the distribution curve) are more favoured.
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