KARYOLOGIC STUDY OF THE CASPIAN MINIATURE HORSE: A BREED WITH SPECIFIC GENETIC CHARACTERISTICS

¹ No 21 Mani Ave.7 Tir Sq. Tehran 1574618741,Iran

It is about four decades that this breed with a history of nearly three thousand years B.C.has been recognized The Caspian miniature horse is an ancient breed of horse, which was thought to be distinct for many years. This breed is a charismatic versatile little horse, existing only in small numbers, has now been recognized as holding an ancestral position in the history of the modern horse breeds, in all probability preceding that of the Arab horse. The evaluation was performed on two completely healthy groups of registered Caspian mares and stallions with 15 heads respectively. Blood samples were obtained and used for metaphase chromosome provide by use of short-term culture. Simple staining and Gimsa banding methods and centromeric banding studied provided chromosomes. Chromosal spreads were photographed and karyotyped. The diploid model of Caspian horse was determined to be 2n=64 and 2n=65 and from those who had 64 chromosomes were obtained 31 autosomal chromosomes that 7 pairs were Meta centric, 6 pairs were submetacentric and 18 pairs were telocentric. Preparations with 65 chromosomes were contained similar chromosomal types except that one extra metacentric chromosome was included. The X sex chromosome was large submetecentric. The Y chromosome was small telocentric. A fusion or fission event can explain this situation Equus Przewalski has extensive chromosome homology with the domestic horse (2n=66). Two acrocentric pairs in E.Przevalski appear to be combined in one Meta centric chromosome (chromosome5) in the E.Caballus karyotyped (2n=64). All breeds within domestic horse species have the same diploid chromosome number (2n=64) with the exception that 2n=65 for the Caspian miniature horse. the extra chromosome could be explained as centric fission of a metacentric chromosome in two acrocentric. Another hypothesis is that the origin followed natural hybridization between domestic horse and Przewalski horse. In cattle and pigs lowered fertility can occur through early embryonic loss from chromosomally unbalanced gametes. Phenotypically normal parents heterozygous for chromosomal fusion between acrocentric chromosomes (Robertsonian translocation or centric fusion) have the potential for producing genetically unbalanced gametes during meiosis. Translocation heterozygotes have seen among the Caspian miniature horses but have not been directly implicated in infertility problems in this breed via different samples which have gathered from different areas of the Caspian sea shores.