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Forty-one cDNA clones of human functional genes were newly mapped to chromosomes of the musk shrew (Suncus murinus, Insectivora) by fluorescence in situ hybridization, and a comparative cytogenetic map of 51 genes, including 10 genes reported in our previous study, was constructed between human (HSA) and musk shrew (SMU) chromosomes. In this comparative map, the 51 genes localized to human autosomes, except HSA 8, 16, and 20, were mapped to 15 shrew autosomes, except SMU 4, 16, 17 and 18. Twelve conserved segments were identified between human and shrew chromosomes, and six segments among the musk shrew, human, and mouse. Our results defined the presence of at least one inversion and several interchromosomal rearrangements that occurred during evolution after the two species diverged from a common ancestor. Localization of three major histocompatibility complex (MHC) genes to shrew chromosome 3 suggested that the MHC genes of the musk shrew are located in a cluster on chromosome 3. The cytogenetic map constructed in this study is the first cytogenetic map with many functional genes in insectivore species. This approach provides clues for clarifying the chromosomal evolution in this order.

In order to construct a chicken (Gallus gallus) cytogenetic map, we isolated 134 genomic DNA clones as new cytogenetic markers from a chicken cosmid DNA library, and mapped these clones to chicken chromosomes by fluorescence in situ hybridization. Forty-five and 89 out of 134 clones were localized to macrochromosomes and microchromosomes, respectively. The 45 clones, which localized to chicken macrochromosomes (Chromosomes 1–8 and the Z chromosome) were used for comparative mapping of Japanese quail (Coturnix japonica). The chromosome locations of the DNA clones and their gene orders in Japanese quail were quite similar to those of chicken, while Japanese quail differed from chicken in chromosomes 1, 2, 4 and 8. We specified the breakpoints of pericentric inversions in chromosomes 1 and 2 by adding mapping data of 13 functional genes using chicken cDNA clones. The presence of a pericentric inversion was also confirmed in chromosome 8. We speculate that more than two rearrangements are contained in the centromeric region of chromosome 4. All 30 clones that mapped to chicken microchromosomes also localized to Japanese quail microchromosomes, suggesting that chromosome homology is highly conserved between chicken and Japanese quail and that few chromosome rearrangements occurred in the evolution of the two species.

This paper reviews studies on sex reversal experiments in chickens, production of sperm bearing a female-specific chromosome, its application for poultry resources and finally a mechanism of sex differentiation of gonads in the chicken.

In birds, females are heterogametic (ZW), while males are homogametic (ZZ). It has been proposed that there is no dosage compensation for the expression of Z-linked genes in birds. In order to examine if the genes are inactivated on one of the two Z chromosomes, we analyzed the allelic expression of the B4GALT1 and CHD-Z genes on Z chromosomes in male chickens. One base substitution was detected among 15 chicken breeds and lines examined for each gene, and cross mating was made between the breeds or lines with polymorphism. cDNAs were synthesized from cultured cell colonies each derived from a single cell of an F1 male embryo. The allelic expression of the B4GALT1 gene was examined by restriction fragment length polymorphism analysis of the PCR products digested with RsaI, and that of the CHD-Z gene by the single nucleotide primer extension (SNuPE) method. Both of the genes displayed biallelic expression, suggesting that these Z-linked genes were not subject to inactivation in male chickens. Comparison between expression levels in males and females by real-time quantitative PCR suggested that expression was compensated for the CHD-Z gene but not for the B4GALT1 gene.