XY1Y2 chromosome system in Salinomys delicatus (Rodentia, Cricetidae)

Abstract

Salinomys delicatus is considered a rare speciesdue to its restricted and patchy distribution, poor recordsand low abundances. It is also the phyllotine with thelowest known diploid chromosome number (2n = 18),however its sex chromosome system has never beendescribed. Here, we studied the chromosomes of sixfemales and three males with bands G, C, DAPI/CMA3 andmeiosis. In males, the chromosome number was 2n = 19,with one large metacentric X-chromosome and two medium-sized acrocentrics absent in females. The karyotype offemales was the same as previously described (2n = 18,FN = 32), with X-chromosomes being metacentric and thelargest elements of the complement. In males, the twoacrocentrics and the large metacentric form a trivalent inmeiotic prophase. This indicates that S. delicatus hasXY1Y2 sex chromosomes, which is confirmed by G andDAPI bands. Constitutive heterochromatin (CH) isrestricted to small pericentromeric blocks in all chromosomes.The X-chromosome shows the largest block ofcentromeric CH, which could favor the establishment ofthis X-autosome translocation. This sex chromosome systemis rare in mammals and, compared with other phyllotinerodents, S. delicatus seems to have undergone a majorchromosome restructuring during its karyotypic evolution.