mass of approximately . Incisors and claws are already formed, but the digits, eyes, and pinnae are closed and cannot be used. The rate at which the young develop differs depending on the distribution range. However, the differences are usually no longer than a day. In Tuva, the pinnae open on the first day of birth and are completely open after three days of development. However, in Mongolia, the same process occurs between two and four days of development. Fur first grows on the crown, back, and abdomen. The young usually have a full coat of fur after seven days of development. Offspring born in captivity have a shorter development time than those born in the wild. Specifically, the growth and development of the head and body, tail, hind feet, and pinnae can be up to a day sooner than those found in the wild. After 28 days of development in captivity, the young are already around half the mass of their parents. In captivity, females become sexually mature at two months of age. The ovarian follicle forms about 16 days prior to the birth of the offspring. After mating, female hamsters typically have larger uteri, ovaries, and adrenal glands compared to females which live alone, with other females or those that have not mated. The females and males may fight each other when getting to know their partner. Also, these females have a shorter gestation period, around four to five days. Hybrids In captivity, only Campbell's dwarf hamsters and Djungarian hamsters are able to interbreed and produce live offspring or hybrids. Although hybrids make suitable pets, the breeding of hybrids and cloning can cause health problems, due to inherited diseases. Because genetic information can be very similar, genetic health problems or vulnerabilities can easily be inherited by the offspring. The widespread breeding and distribution of hybrids could threaten the existence of both pure species and subspecies of the ecosystem. This could ultimately lead to the extinction of the subspecies. Each litter becomes smaller as more generations are produced and the young commonly begin to inherit many congenital problems. The two species of Phodopus hamsters (P. sungorus and P. campbelli) have the same number of chromosomes, and the chromosomes are similar in terms of size and morphology. However, several chromosomes show structural differences in the location and size of C-heterochromatin blocks. In nature, the two species do not meet, but