Обновление! Суперпуперкот на снимке снизу вчера встретил своего суперпуперхозяина и сьехал от мамы. Налетайте, остался единственный экземпляр! Согласно википедии такой кот рождается один на три тысячи штук!
http://en.wikipedia.org/wiki/Tortoiseshell_cat#Genetics
Male cats, like other mammalian males, have only a single X chromosome (XY) that does not undergo X-inactivation: coat color is determined by which allele is present on the X, and they will be either entirely black or orange. Very rarely (approximately 1 in 3,000[5]) a male tortoiseshell or calico is born. These animals typically have an extra X chromosome (XXY), a condition known in humans as Klinefelter syndrome, and undergo an inactivation process like that in females. As in humans, these cats are sometimes sterile because of the imbalance in sex chromosomes. Some male calico or tortoiseshell cats may be chimeras, which result from the fusion in early development of two embryos with different color genotypes. Others are mosaics, in which the XXY condition arises after conception and the cat is a mixture of cells with different numbers of X chromosomes. Simply said they are melanistic calicos meaning saturation of color.
Вольный перевод - у таких котов-мужиков лишняя X-хромосома. Временами они из-за этого стерильны. Некоторые из них могут быть химерами, получившимися из-за слияния на начальном этапе развития эмбрионов с разными генотипами. Похоже, наш случай =)