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In evolutionary biology, disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups.
Genetic divergence will always accompany reproductive isolation, either due to novel adaptations via selection and/or due to genetic drift, and is the principal mechanism underlying speciation. On a molecular genetics level, genetic divergence is due to changes in a small number of genes in a species, resulting in speciation . [ 2 ]
Genetic hitchhiking is often considered the opposite of background selection. genetic load Any reduction in the mean fitness of a population owing to the existence of one or more genotypes with lower fitness than that of the most fit genotype. [1] genetic testing. Also DNA testing and genetic screening.
Passive versus active trends in complexity. Organisms at the beginning are red. Numbers are shown by height with time moving up in a series. If evolution possessed an active trend toward complexity (orthogenesis), as was widely believed in the 19th century, [12] then we would expect to see an active trend of increase over time in the most common value of complexity among organisms.
When we have served our purpose we are cast aside. But genes are denizens of geological time: genes are forever. [83] Others view selection working on many levels, not just at a single level of organism or gene; for example, Stephen Jay Gould called for a hierarchical perspective on selection. [84]
Gene selection acts directly at the level of the gene. In kin selection and intragenomic conflict, gene-level selection provides a more apt explanation of the underlying process. Group selection, if it occurs, acts on groups of organisms, on the assumption that groups replicate and mutate in an analogous way to genes and individuals. There is ...
The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged.The biomolecular data used for such calculations are usually nucleotide sequences for DNA, RNA, or amino acid sequences for proteins.
The rate of evolution is quantified as the speed of genetic or morphological change in a lineage over a period of time. The speed at which a molecular entity (such as a protein, gene, etc.) evolves is of considerable interest in evolutionary biology since determining the evolutionary rate is the first step in characterizing its evolution. [1]