Natural Selection and Evolutionary Concepts

Study Notes

Directional Selection: Favours extreme phenotypes, leading to shifts in allele frequencies over time toward that phenotype.
Stabilizing Selection: Reduces genetic diversity, stabilizing the population mean for a particular trait.
Disruptive Selection: Favours extreme trait values over intermediate ones, promoting diversity in a population.

Uniformitarianism: Theory that geological changes occur through continuous and uniform processes over time.
Variational Evolution: Involves continual branching and extinction of species; differs from transformational evolution, which follows a simple, linear path.
Transformational Evolution: Refers to linear changes in a single lineage, contrasting with the branching nature of variational evolution.

Adaptive Radiation: Diversification of organisms into different forms to exploit various ecological niches.
Homoplasy: Shared traits among different species not present in their common ancestor, often due to convergent evolution.

Ecological Release: Occurs when a species is introduced to a new environment, leading to establishment or extinction.
Sessile: Describes organisms, such as barnacles, that are fixed in one place and unable to move.

Punctuated Equilibrium: Suggests that species experience long periods of stability (stasis) interrupted by brief, significant changes.

Alcohol Dehydrogenase: Enzyme responsible for breaking down alcohol; absence can lead to addiction.
Founder Effect: Occurs when a small group lacks a specific gene, resulting in its absence in the larger population.
Gene Flow: Transfer of alleles between populations, potentially causing notable changes in allele frequencies.
Genetic Drift: Random changes in gene frequencies, especially significant in small populations due to chance events.
Pleiotropy: A single gene affecting multiple traits, leading to diverse phenotypic expressions.
Hitch-hiking Alleles: Alleles that change frequency not due to natural selection but because of proximity to another gene under selection.
Haplotype: A combination of DNA variations inherited together, indicating the presence of linked alleles or SNPs on the same chromosome.