Population Genetics: Evolution and Inheritance

Introduction to Population Genetics

• Mendel's principles of genetic inheritance were unnoticed during his lifetime.
• Darwin published his theory of natural selection six years before Mendel's paper on heredity.
• Darwin's failure to explain inheritance made his theory incomplete, and a unifying theory had to wait until the 1930s.
• In 1900, Mendel's work was rediscovered, leading to its widespread recognition.
• Initially, Mendel's theory appeared to conflict with Darwin's, causing a divide among scientists.

Unifying Theories

• In the 1920s, scientists aimed to reconcile Darwin's and Mendel's theories.
• Ronald A. Fisher, J. B. S. Haldane, and Sewall Wright created population genetics, unifying the theories.
• Population genetics showed how traits' inheritance leads to evolution by natural selection.
• Theodosius Dobzhansky and Ernst Mayr applied population genetics to natural populations.
• Population genetics expanded into the Modern Evolutionary Synthesis, which underpins all biological sciences.
• Fisher, Haldane, and Wright connected Mendel's principles to biology through population genetics.

Population Genetics Explained

• Population genetics explains mathematically how evolution functions.
• Darwin identified natural selection but missed inheritance and a mathematical predictive theory.
• Population genetics is essentially an updated theory of evolution.

Key Terms in Population Genetics

• Population/Mendelian population: A group of individuals of the same species with equal chances to interbreed.
• Gene pool: The mix of alleles for each gene within a population.
• Genotypic frequency: The percentage of individuals with a particular genotype, calculated as f(AA) = (# of AA individuals/N).
• Allelic frequency: The percentage of alleles of a specific type in a population.
  • Calculated considering that each individual in a diploid species carries two alleles (2N).
• Example: In a population of 100 with gene A having alleles A and a:
  • 20 individuals are AA, 30 are aa, and 50 are Aa.
  • The number of A alleles is (2 x 20) + 50 = 90.
• The frequency of allele A is f(A) = (2 x #AA + #Aa)/2N.
• The frequency of allele a is f(a) = (2 x #aa + #Aa)/2N.
  • f(A) = (2 x 20 + 50) / 2(100) = 0.45
  • f(a) = (2 x 30 + 50) / 2(100) = 0.55
• Frequencies are expressed as decimals, totaling 1.
• In population genetics:
  • p = frequency of the first allele.
  • q = frequency of the second allele:
• Formulas
  • p = f(A) = (2 x #AA + #Aa)/2N
  • q = f(a) = (2 x #aa + #Aa)/2N
  • p + q = 1
• A gene pool's allele frequency varies by generation within a species.
• Evolution: The change in allele frequencies from one generation to the next.
  • Evolution occurs if an allele frequency for any gene in the population differs from one generation to the next.
• Evolution occurs in populations, not individuals, over generations, altering a gene pool.
• Each gene in a population can evolve independently.

Hardy-Weinberg Theorem

• The understanding of population and evolution allows an examination of forces causing evolution and their specifics, based on the Hardy-Weinberg Theorem.

Explore the principles of population genetics, which reconcile Darwin's theory of evolution with Mendel's laws of inheritance. Discover how scientists like Fisher, Haldane, and Wright unified these concepts. Learn how natural selection acts on heritable traits within populations.