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Polyploidy occurs in some tissues of animals that are otherwise diploid, such as human muscle tissues. [45] This is known as endopolyploidy. Species whose cells do not have nuclei, that is, prokaryotes, may be polyploid, as seen in the large bacterium Epulopiscium fishelsoni. [46] Hence ploidy is defined with respect to a cell.
It is possible on rare occasions for ploidy to increase in the germline, which can result in polyploid offspring and ultimately polyploid species. This is an important evolutionary mechanism in both plants and animals and is known as a primary driver of speciation . [ 8 ]
The list of organisms by chromosome count describes ploidy or numbers of chromosomes in the cells of various plants, animals, protists, and other living organisms.This number, along with the visual appearance of the chromosome, is known as the karyotype, [1] [2] [3] and can be found by looking at the chromosomes through a microscope.
Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants. [6] [7] Sexual reproduction also occurs in some unicellular eukaryotes. [2] [8] Sexual reproduction does not occur in prokaryotes, unicellular organisms without cell nuclei, such as bacteria and archaea.
Human reproduction naturally takes place as internal fertilization by sexual intercourse. During this process, the man inserts his erect penis into the woman's vagina and then either partner initiates rhythmic pelvic thrusts until the man achieves orgasm , which leads to ejaculation of semen containing sperm into the vaginal canal.
Once a polyploid is made, either synthetically or naturally, the genome goes through a period of "genome shock". Genome shock can be defined as a stage in which the genome experiences massive reorganization and structural changes to deal with the external stress (X-ray damage, chromosome duplication, etc.) imposed upon the genome. [ 7 ]
Endoreduplication, endomitosis and polytenization are three different processes resulting in polyploidization of a cell in a regulated manner. In endoreduplication cells skip M phase completely by exiting the mitotic cell cycle in the G 2 phase after completing the S phase several times, resulting in a mononucleated polyploid cell.
A polyploid complex, also called a diploid-polyploid complex, is a group of interrelated and interbreeding species that also have differing levels of ploidy that can allow interbreeding. A polyploid complex was described by E. B. Babcock and G. Ledyard Stebbins in their 1938 monograph The American Species of Crepis : their interrelationships ...