This contrasts with classical genetics, which works mostly on crosses between laboratory strains, and DNA sequence analysis, which studies genes at the molecular level.
[1] Examples of such traits include flowering time, drought tolerance, polymorphism, mimicry, and avoidance of attacks by predators.
Natural selection acts on existing genetic variation, favouring alleles that enhance survival and reproduction.
Adaptation occurs when beneficial alleles increase in frequency due to selective pressures, such as changes in climate, predation, or resource availability.
Fisher helped form what is known as the modern synthesis of ecology, by mathematically merging the ideas of Darwin and Mendel.
He and his colleagues carried out studies on natural populations of Drosophila species in western USA and Mexico over many years.
Cain were all strongly influenced by Ford; their careers date from the post World War II era.
Collectively, their work on lepidoptera and on human blood groups established the field and threw light on selection in natural populations, where its role had been once doubted.
It was demonstrated in the early 1910s, and again in many later studies, that the melanic variants were a result of dominant alleles at a single locus in the B. betularia genome.
[14][15] These experiments, while inititally unsuccessful, found that when a variety of insects are provided, the birds did preferentially prey on the most conspicuous moths: those with coloration unmatched to their surroundings.
Kettlewell then performed field experiments using mark-recapture techniques to investigate the selective predation of moths in their natural habitat.
The use of molecular marking and chromosomal mapping in conjunction with population surveys demonstrated in the early 2010s that the melanic B. betularia variants have one single ancestral origin.
The way that complex traits with continuous variation change in response to natural selection can most reasonably be explained by many alleles having a small effect on the phenotype of interest.