Selection

• Dual Level Operation: Selection operates at two interrelated levels: the organism level and the allele level.
• Mechanism: Organisms that are physically, physiologically, and behaviorally better adapted to their environment survive and reproduce. Less adapted organisms either die or fail to reproduce.
• Key Processes: It operates through differential mortality (survival rates) and differential reproductive potential (breeding success).

• Limiting Factors: As population size increases, environmental resources (like food for animals or light for plants) become limited, leading to competition.
• Competitive Advantage: Organisms possessing traits that provide an advantage will successfully secure resources, survive, and pass those characteristics to the next generation.
• Selection Pressure: The combination of environmental limiting factors and population size creates selection pressure of varying intensity.

• Selection determines exactly which alleles are passed to the next generation based on the advantages they provide when expressed physically (phenotypes).
• Selection pressure alters the gene pool by increasing or decreasing the spread of specific alleles. These shifts in allele frequency ultimately lead to evolutionary change.

Major genetic changes stem from mutant alleles spreading through the gene pool. The timing of this selection depends on the nature of the allele:

• Dominant Alleles: Instantly appear in the phenotype and undergo immediate selection.
• Recessive alleles (Which constitute most mutations) remain hidden from selection until they are inherited in a homozygous state and finally expressed in the phenotype.

• Selection favours the survival and reproduction of organisms that are physically, physiologically, and behaviorally best adapted to their environment.
• Competition for limited environmental resources generates selection pressure, driving differential mortality and reproductive success within a population.
• The process actively dictates which alleles are transmitted to subsequent generations based on the phenotypic advantages they confer.
• Evolutionary change occurs as selection pressure alters the frequency of specific alleles within the population's overall gene pool.
• Dominant mutant alleles undergo immediate selection, whereas recessive alleles remain unselected until they are expressed in a homozygous condition.