It occurs in the somatic cells of some animals, such as goldfish, salmon, and salamanders, but is especially common among ferns and flowering plants (see Hibiscus rosa-sinensis), including both wild and cultivated species. Wheat, for example, after millennia of hybridization and modification by humans, has strains that are diploid (two sets of chromosomes), tetraploid (four sets of chromosomes) with the common name of durum or macaroni wheat, and hexaploid (six sets of chromosomes) with the common name of bread wheat. Many agriculturally important plants of the genus Brassica are also tetraploids. Sugarcane can have ploidy levels higher than octaploid.Polyploidization can be a mechanism of sympatric speciation because polyploids are usually unable to interbreed with their diploid ancestors. An example is the plant Erythranthe peregrina. Sequencing confirmed that this species originated from E. × robertsii, a sterile triploid hybrid between E. guttata and E. lutea, both of which have been introduced and naturalised in the United Kingdom. New populations of E. peregrina arose on the Scottish mainland and the Orkney Islands via genome duplication from local populations of E. × robertsii. Because of a rare genetic mutation, E. peregrina is not sterile. Terminology
Types
Polyploid types are labeled according to the number of chromosome sets in the nucleus.
The mass effect of ovarian tumors is also a common cause of torsion. Torsion of the ovary usually occurs with torsion of the fallopian tube as well on their shared vascular pedicle around the broad ligament, although in rare cases the ovary rotates around the mesovarium or the fallopian tube rotates around the mesosalpinx. In 80%, torsion happens unilaterally, with slight predominance on the right. In ovarian torsion, the ovary rotates around both the infundibulopelvic ligament (ie, suspensory ligament) and the utero-ovarian ligament (i.e. ovarian ligament), disrupting blood flow to the ovary. Diagnosis
Ovarian torsion is difficult to diagnose accurately, and operation is often performed before certain diagnosis is made. A study at an  obstetrics and gynaecology department found that preoperative diagnosis of ovarian torsion was confirmed in only 46% of people. Ultrasound
Gynecologic ultrasonography is the imaging modality of choice. Use of doppler ultrasound  in the diagnosis has been suggested. However, doppler flow is not always absent in torsion – the definitive diagnosis is often made in the operating room.Lack of ovarian blood flow on doppler sonography seems to be a good predictor of ovarian torsion. Women with pathologically low flow are more likely to have torsion. The sensitivity and specificity of abnormal ovarian flow are 44% and 92%, respectively, with a positive and negative predictive value of 78% and 71%, respectively. Specific flow features on Doppler sonography include:
Little or no intra-ovarian venous flow. This is commonly seen in ovarian torsion. Absent arterial flow.