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Coalescent theory is a model of how alleles sampled from a population may have originated from a common ancestor. In the simplest case, coalescent theory assumes no recombination , no natural selection , and no gene flow or population structure , meaning that each variant is equally likely to have been passed from one generation to the next.
Human diploid cells have 46 chromosomes (the somatic number, 2n) and human haploid gametes (egg and sperm) have 23 chromosomes (n). Retroviruses that contain two copies of their RNA genome in each viral particle are also said to be diploid. Examples include human foamy virus, human T-lymphotropic virus, and HIV. [29]
The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. In the germ-line (the sex cells) the chromosome number is n (humans: n = 23). [4] [5] p28 Thus, in humans 2n = 46. So, in normal diploid organisms, autosomal chromosomes are present in two copies.
According to the neutral theory of molecular evolution, a neutral allele remains in a population for Ne generations, where Ne is the effective population size. An idealised diploid population will have a pairwise nucleotide diversity equal to 4 μ {\displaystyle \mu } Ne, where μ {\displaystyle \mu } is the mutation rate.
The mutational hazard hypothesis is a non-adaptive theory for increased complexity in genomes. [32] The basis of mutational hazard hypothesis is that each mutation for non-coding DNA imposes a fitness cost. [33] Variation in complexity can be described by 2N e u, where N e is effective population size and u is mutation rate. [34]
Dihedral groups are among the simplest examples of finite groups, and they play an important role in group theory and geometry. The notation for the dihedral group differs in geometry and abstract algebra. In geometry, D n or Dih n refers to the symmetries of the n-gon, a group of order 2n. In abstract algebra, D 2n refers to this same dihedral ...
After the pollen tube enters the gametophyte, the pollen tube nucleus disintegrates and the two sperm cells are released; one of the two sperm cells fertilises the egg cell (at the bottom of the gametophyte near the micropyle), forming a diploid (2n) zygote. This is the point when fertilisation actually occurs; pollination and fertilisation are ...
The neutral theory assumes that most mutations that are not deleterious are neutral rather than beneficial. Because only a fraction of gametes are sampled in each generation of a species, the neutral theory suggests that a mutant allele can arise within a population and reach fixation by chance, rather than by selective advantage. [1]