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In 2014, Lee, Langley, and Begun conducted another research study related to gene fixation. They focused on Drosophila melanogaster population data and the effects of genetic hitchhiking caused by selective sweeps. Genetic hitchhiking occurs when one allele is strongly selected for and driven to fixation.
Processes of natural selection such as sexual, convergent, divergent, or stabilizing selection pave the way for allele fixation. One way some of these natural selection processes cause fixation is through one specific genotype or phenotype being favored, which leads to the convergence of the variability until one allele becomes fixed.
In small populations, fixation can occur in just a few generations. In this simulation, each black dot on a marble signifies that it has been chosen for copying (reproduction) one time. Fixation in the blue "allele" occurs within five generations.
A selective sweep can occur when a rare or previously non-existing allele that increases the fitness of the carrier (relative to other members of the population) increases rapidly in frequency due to natural selection. As the prevalence of such a beneficial allele increases, genetic variants that happen to be present on the genomic background ...
The individuals without the genes are therefore disfavored, and the favorable genes spread in the population by the death (or lowered fertility) of the individuals without the genes. Note that Haldane's model as stated here allows for more than one gene to move towards fixation at a time; but each such will add to the cost of substitution.
The Y chromosome does not undergo recombination, making it particularly prone to the fixation of deleterious mutations via hitchhiking. This has been proposed as an explanation as to why there are so few functional genes on the Y chromosome.
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Another model happening when multiple beneficial mutations independently occur in short succession of one another — consequently, a second copy occur through mutation before the selective fixation of the first copy. [3] Soft sweeps can occur from both standing variation and rapidly repeating beneficial mutations. [4] [5] [6]