A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two common sexes and a few less common intersex variations.
The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining because it is the presence or absence of Y chromosome that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the SRY gene, which triggers development of male gonads. The Y chromosome is passed only from male parents to male offspring.
The XO sex-determination system is a system that some species of insects, arachnids, and mammals use to determine the sex of offspring. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome (XO), while females have two (XX). The letter O signifies the lack of a Y chromosome. Maternal gametes always contain an X chromosome, so the sex of the animals' offspring depends on whether a sex chromosome is present in the male gamete. Its sperm normally contains either one X chromosome or no sex chromosomes at all.
Tokudaia is a genus of murine rodent native to Japan. Known as Ryūkyū spiny rats or spinous country-rats, population groups exist on several non-contiguous islands. Despite differences in name and appearance, they are the closest living relatives of the Eurasian field mouse (Apodemus). Of the three species, both T. osimensis and T. tokunoshimensis have lost their Y chromosome and SRY gene; the sex chromosomes of T. muenninki, on the other hand, are abnormally large.
Robert's spiny-rat or Para spiny rat, is a spiny rat species found in Brazil. This species is named after the collector Alphonso Robert, who collected the holotype of this species in 1901.
Elias's Atlantic spiny-rat or the Rio de Janeiro spiny rat, is a spiny rat species from South America. It is found in Brazil.
Tome's spiny rat, also known as Tomes' spiny rat or the Central American spiny rat, is a species of spiny rat distributed from Honduras to Ecuador. The IUCN has assessed its conservation status as being of "least concern".
The Yanbaru whiskered bat(Myotis yanbarensis) is a species of vesper bat in the genus Myotis.
The Ryukyu long-tailed giant rat or Ryukyu rat is a species of rodent in the family Muridae. It is the only extant species in the genus Diplothrix. It is found only in the Ryukyu Islands of Japan. Its natural habitat is temperate forests.
Ellobius is a genus of rodents in the family Cricetidae. It is the only member of the tribe Ellobiusini. It contains two of the handful of examples of mammal species that have lost the Y chromosome.
The southern mole vole is a species of rodent in the family Cricetidae. It is found in Afghanistan, Iran, Pakistan, and Turkmenistan.
The Transcaucasian mole vole is a species of rodent in the family Cricetidae.
The northern mole vole is a species of rodent in the family Cricetidae. It is distributed over large parts of Eastern Europe and Asia.
The Zaisan mole vole, or eastern mole vole, is a species of rodent in the family Cricetidae. It is found in central Asia.
The red spiny rat, also known as the Indomalayan maxomys, is a rodent species in the family Muridae that inhabits forests in Myanmar, Thailand, Malaysia, Cambodia, Laos, Vietnam and on the islands of Java, Borneo and Sumatra. In China, it has been recorded only in southernmost Yunnan.
Muennink's spiny rat or Okinawa spiny rat is a species of rodent in the family Muridae. Endemic to Okinawa Island, Japan, its natural habitat is subtropical moist broadleaf forest. The karyotype has 2n = 44. Its sex chromosomes are abnormally large, while the other two species in Tokudaia have lost their Y chromosome. It is found only on the northern part of the island, above 300 m, and is thought to inhabit an area of less than 3 km2.
The Ryukyu spiny rat is a species of rodent in the family Muridae. Endemic to Amami Ōshima island in the Amami Islands of the Ryukyu archipelago of Japan, its natural habitat is subtropical moist broadleaf forest. The karyotype has an odd diploid number, 2n = 25. Like its relative T. tokunoshimensis, it has lost its Y chromosome and SRY gene.
The pallid Atlantic tree-rat is a species of rodent in the family Echimyidae. It is a species of spiny rat. It is endemic to Brazil, where it is found from Paraiba to Minas Gerais.
The black-spined Atlantic tree-rat,, is a South American spiny rat species in the family Echimyidae. It is found in southeastern Brazil, where it inhabits moist broadleaf forest and semideciduous forest in the Atlantic Forest region. It is arboreal and is believed to build nests of leaves in trees. Its karyotype has 2n=52.
Apodemini is a tribe of muroid rodents in the subfamily Murinae. It contains two extant genera, one found throughout Eurasia and the other endemic to the Ryukyu Islands. Several fossil genera are also known from throughout Eurasia, including one large species (Rhagamys) that persisted on Sardinia and Corsica up until at least the first millennium BC, when it was likely wiped out by human activity.
