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However, it is possible for directional selection to take a very long time to find a local optimum on a fitness landscape. [29] A possible example of long-term directional selection is the tendency of proteins to become more hydrophobic over time, [30] and to have their hydrophobic amino acids more interspersed along the sequence. [31]
The incidental purging of non-deleterious alleles due to such spatial proximity to deleterious alleles is called background selection. [4] This effect increases with lower mutation rate but decreases with higher recombination rate. [5] Purifying selection can be split into purging by non-random mating (assortative mating) and purging by genetic ...
Another example is plant self-incompatibility alleles. When two plants share the same incompatibility allele, they are unable to mate. Thus, a plant with a new (and therefore, rare) allele has more success at mating, and its allele spreads quickly through the population. [9] A similar example is the csd alleles of the honey bee. A larva that is ...
A heated debate arose when Kimura's theory was published, largely revolving around the relative percentages of polymorphic and fixed alleles that are "neutral" versus "non-neutral". A genetic polymorphism means that different forms of particular genes, and hence of the proteins that they produce, are co-existing within a species.
The peacock tail in flight, the classic example of an ornament assumed to be a Fisherian runaway. Fisherian runaway or runaway selection is a sexual selection mechanism proposed by the mathematical biologist Ronald Fisher in the early 20th century, to account for the evolution of ostentatious male ornamentation by persistent, directional female choice.
This is an example of balancing selection between the fierce selection against homozygous sickle-cell sufferers, and the selection against the standard HgbA homozygotes by malaria. The heterozygote has a permanent advantage (a higher fitness) wherever malaria exists.
Evolutionary progress as a tree of life. Ernst Haeckel, 1866 Lamarck's two-factor theory involves 1) a complexifying force that drives animal body plans towards higher levels (orthogenesis) creating a ladder of phyla, and 2) an adaptive force that causes animals with a given body plan to adapt to circumstances (use and disuse, inheritance of acquired characteristics), creating a diversity of ...
This category is for articles about scientific hypotheses in the realm of biology. Subcategories This category has the following 10 subcategories, out of 10 total.