Shahram Dordari1 , Reza Mehran Nezhad1

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.

Ovan text i originalsammanhang:: PAG-XII (W72) KARYOLOGIC STUDY OF THE CASPIAN MINIATURE HORSE A BREED WITH SPECIFIC GENETIC CHARACTERISTICS Shahram D.html

The group of Caspian ponies studied contained some animals with 65 chromosomes and others with 64 chromosomes. The morphology and G-banding pattern of the chromosomes resembled those of Equus caballus and E. przewalskii. The karyogram of animals with 65 chromosomes was identical to that of the cross between E. caballus and E. przewalskii. It is suggested that the Caspian pony is the product of natural hybridization between E. caballus and E. prezwalskii. Low reproductive effeciency of the Caspian pony is suggested as the cause of decline in the population of these animals.

Journal of Reproduction and Fertility (1979) 57 331-333
© 1979 Society for Reproduction and Fertility
DOI: 10.1530/jrf.0.0570331

Re: [CaspianHorse] Re: Caspian Genetics /spotty horses etc

Dear friends

The Caspian horse karyotype has been done 2 times by Dr.Monazah & Pandit 1979, Mehrannezhad & me on 2003.On both of them there were some 65 Chromosome number Caspians.I shared this idea with Dr.Cothran and he was interested on it by as he always used the hair samples(and it is necessary to use white blood cells for karyoytyping) it was not possible for him to do it. So I prepared a project and shared it to some of the universities to do it.I have applied and searching for the fundings of this big project to start it by new year.

The summary and literature review of this project will help you to know what is going on now:

Caspian horse Karyotype project:

The horse (Equus caballus) is a member of the order Perissodactyla of odd toed mammals made up by the three families:

Equidae (two horse species, three hemione species, two donkey species and at least three zebra species), Rhinocerotidae (five species) and Tapiridae (four species). Among the Perissodactyla, only three species have been domesticated: the horse (Equus caballus) and the two donkeys (Equus asinus and Equus africanus somalicus).

Hybrids have been produced for most species pairs among the Equidae, however the hybrids are almost always infertile. The best known hybrid is the cross of the horse mare with a donkey jack to produce a mule. Mules were prized for their intelligence and vigor and played a major role in agriculture and industry. The reason for the infertility is probably differences in genome organization between the species of Equidae and failure of meiosis within hybrid animals. Chromosome numbers range from 33 pairs for Equus przewalskii (Mongolian Wild Horse) to 16 pairs for the Equus zebra hartmannae (Hartmann’s zebra, a.k.a., Mountain zebra). These species diverged 3-5 million years ago, so chromosome evolution has been relatively rapid for this family. Comparative mapping studies indicate that chromosome evolution among the Equidae has probably been the result of chromosome fusion and centromere repositioning (Lear, 2005 ;)

The living wild horse species to day are found only in Asia and Africa. Chromosomal morphology and numbers in the living members of the genus Equus present a heterogeneous picture. As an illustration of this diversity, we can remind the Chromosome number of some species and some subspecies as:

(Ryder et al.1987, Benirschke &Ryder 1985, Bowling&Million 1988)

Numerical as well as morphological chromosomal differences show that the specification process in equines involved exchanges of DNA sequence blocks in many chromosomes.

Despite the array of numerical and structural differences, several prominent chromosomal similarities are found, particularly within the horses, the asses and the half-asses   (hemiones).

As the genetic of all domestic breeds of horses is nearly identified. Horses of all breeds have the same number, size and shape of chromosomes (Except the Caspian miniature horse).

The current standard karyotype for the horses was defined by Richer and colleagues (1990).It consists of 13 meta- and submetacentric (bi-armed) and 18 acrocentric pairs of autosomes, plus a large submetacentric X and a small acrocentric Y.

Przewalski’s horse has extensive chromosome homology with the domestic horse. Two acrocentric pairs in E przewalski appear to be combined in one metacentric chromosome (chromosome 5) in the E.caballus karyotype (E. Ahrens, G. Stranzinger 2005).

A Robertsonian translocation event can explain the difference between the two species; either fusion or fission is possible, assuming one species is derived from the other, depending on which arrangement is ancestral.

Cytogenetic map: The equine gene mapping community has published extensively to rapidly expand the cytogenetic map in the horse (e.g.,  Breen et al. 1997; Goddard et al. 2000; Lear et al. 2001; Lindgren et al., 2001; Mariat et al. 2001; Raudsepp et al. 2001; Milenkovic et al. 2002; Chowdhary et al. 2002; Raudsepp et al. 2002; Chowdhary et al. 2003; Lee et al. 2004; Raudsepp et al. 2004; Raudsepp et al. 2004; Brinkmeyer-Langford et al. 2005; Gustafson-Seabury et al. 2005,).

All breeds within the domestic horse species have the same chromosome number (2n=64), with the exception that 2n=65 has been reported for some Caspian horses (Hatami-Monazah & Pandit 1979, Mehrannezhad & Dordari 2003).

The extra chromosome could be explained as centric fission of a metacentric chromosome into two acrocentrics, although the authors suggested that the origin followed natural hybridization between domestic horses and Przewalski’s horse.

In the 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 have the potential for producing genetically unbalanced gametes during meiosis? Translocation heterozygotes are reported among the Caspian horses but have not been directly implicated in infertility problems in this breed (Hatami-Monazah & Pandit 1979).

Power (1991) described an 11 years old Thoroughbred mare with only two foals in eight years of breeding that had abnormal Karyotype consisting of heterozygosity for a balanced reciprocal translocation between two of the largest autosomes.

Eight years old fertile Thoroughbred stallion with a balanced tandem translocation between chromosomes 1 and 30 was reported by Long (1994).Mares bred to this stallion would become pregnant, but lose the pregnancy in an early embryonic death.

The karyotype of 10 mares which showed abnormal fertility due to anoestrus, repeat breeding, abortion or underdevelopment of internal reproductive organs showed: X chromosome monosomy was diagnosed in five mares; 63,X karyotype in pure form in one mare, and 63,X/64,XX karyotype in the form of mosaic cell lines in the other four mares with a low (3.5-9%) proportion of lines with an abnormal set of chromosomes by  Bugno et al (2003).

Comparative chromosomal studies of E. caballus (ECA) and E. przewalskii (EPR) in a female F1 hybrid by Ahrens, E. & Stranzinger, G. (2005)showed that the karyotype of   E. caballus and E. przewalskii differ solely by one Robertsonian translocation (ECA 5 =EPR 23 + EPR 24).

 So the aim of this research could be to clear that if we join 2 Caspian horse with 65 chromosome number will join to each other and we can separate the semen of the stallion which will have the 33 chromosomes number and the ovum of the same chromosome  (33) the next generation will be 66 ( like the E. przewalskii  )or not and will be able to survive and if it will be sterile or not.

Let me know if you can help us to do this project please.

Shahram