Population Genetics Overview

Population Genetics

• Aims to understand how various forces, including mutation, genetic drift, migration, inbreeding, and selection, shape the genetic makeup of populations over time.
• Provides a mathematical framework to study allele frequency changes.
• Explores how genetic diversity is maintained or altered in populations.

Genetic Drift

• Random fluctuations in allele frequencies due to chance events.
• More pronounced in small populations: leading to potential fixation or loss of alleles, reducing genetic variation.
• Bottleneck Effect is a type of genetic drift where a population experiences a drastic reduction in size due to a random event.

Migration (Gene Flow)

• The movement of individuals or their genes between populations.
• Introduces new alleles into a population, increasing genetic diversity.
• Counteracts the effects of genetic drift.

Inbreeding

• Occurs when individuals mate with relatives.
• Leads to an increase in homozygosity, reducing genetic diversity.
• Can lead to inbreeding depression by exposing deleterious recessive alleles.

Selection

• Differential survival and reproduction based on genotype.
• Natural selection favors alleles that confer a fitness advantage.
• Deleterious alleles may be purged from the population.
• Can either increase or decrease genetic variation depending on the type of selection: (directional, stabilizing, or disruptive).

Hardy-Weinberg Principle

• Fundamental concept in population genetics.
• States that in the absence of evolutionary forces (genetic drift, migration, inbreeding, and selection), allele and genotype frequencies remain constant for generations.
• Assumes random mating, no mutations, no migration, infinite population size, and no natural selection.
• Equation: p^2 + 2pq + q^2 = 1
• p+q=1
• p = dominant allele frequency
• q = recessive allele frequency

Evolution

• Process by which populations of organisms change over time through alterations in allele frequencies.
• Results from natural selection, genetic drift, gene flow, and mutation.
• Leads to adaptation, speciation, and the diversity of life.

Lamarck's Theory (Lamarckism)

• Proposed that organisms evolve by inheriting acquired traits.
• Traits acquired during an organism's lifetime can be passed to offspring.
• Example: Giraffes stretching their necks to reach leaves, resulting in offspring with longer necks.
• Lacked a mechanism for inheritance.

Darwin's Theory (Darwinism)

• Based on natural selection.
• Individuals with advantageous traits are more likely to survive and reproduce.
• These traits are then inherited by the next generation, leading to evolutionary changes over time.

Key Difference between Lamarck and Darwin

• Lamarck believed in the inheritance of acquired traits.
• Darwin proposed the inheritance of traits through genetic variation and natural selection.

Scientific Evidence for Lamarck and Darwin

• Lamarck had little empirical evidence but based his ideas on the observed progression of complexity in organisms.
• Darwin accumulated a vast amount of evidence through his travels and observations. He collected data on the finches and tortoises of the Galápagos Islands, which provided strong support for his theory.