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[3]: 126 The most common example is sexual dimorphism, which occurs in many organisms. Other examples are mimetic forms of butterflies (see mimicry), and human hemoglobin and blood types. According to the theory of evolution, polymorphism results from evolutionary processes, as does any aspect of a species.
In 1973, M. J. D. White, then at the end of a long career investigating karyotypes, gave an interesting summary of the distribution of chromosome polymorphism. "It is extremely difficult to get an adequate idea as to what fraction of the species of eukaryote organisms actually are polymorphic for structural rearrangements of the chromosomes.
A study conducted by the National Science Foundation in 2007 found that genetic diversity (within-species diversity) and biodiversity are dependent upon each other — i.e. that diversity within a species is necessary to maintain diversity among species, and vice versa. According to the lead researcher in the study, Dr. Richard Lankau, "If any ...
The differences of the amount of heterochromatin among congeneric rodent species may reach 33% of nuclear DNA in Dipodomys species, [13] 36% in Peromyscus species, [14] 42% in Ammospermophilus [15] and 60% in Thomomys species where C-value (haploid DNA content) ranges between 2.1 and 5.6 pg. [16] [17]
The evolution of biological complexity is one important outcome of the process of evolution. [1] Evolution has produced some remarkably complex organisms – although the actual level of complexity is very hard to define or measure accurately in biology, with properties such as gene content, the number of cell types or morphology all proposed as possible metrics.
Polymorphisms can be identified in the laboratory using a variety of methods. Many methods employ PCR to amplify the sequence of a gene. Once amplified, polymorphisms and mutations in the sequence can be detected by DNA sequencing, either directly or after screening for variation with a method such as single strand conformation polymorphism analysis.
Population bottleneck followed by recovery or extinction. A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as genocide, speciocide, widespread violence or intentional culling.
Müllerian mimetic species of Heliconius from South America Harmless scarlet kingsnake mimics the coral snake, but its pattern varies less where the coral snake is rare. Positive frequency-dependent selection gives an advantage to common phenotypes. A good example is warning coloration in aposematic species. Predators are more likely to ...