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Cytogenetic studies of three equine hybrids.

Abstract: A detailed investigation of testicular meiosis in a mule, a hinny and a Przewalski horse/domestic horse hybrid were made. Abnormalities of pairing were observed in the mule and hinny in most germ cells at the pachytene stage of meiotic prophase, and spermatogenesis was alsmot totally arrested. A few mature spermatozoa were recovered from the ejaculate and epididymal flushings of the hinny. The Przewalski horse/domestic horse hybrid was fertile and showed normal spermatogenesis. Chromosome banding studies showed a close homology between the karyotypes of the Prezwalski horse (Equus przewalskii, 2n = 66) and the domestic horse (E. caballus, 2n = 64), and it is evident that a single Robertsonian translocation has occurred transforming four acrocentric chromosomes of E. przewalskii into two metacentric chromosomes in E. caballus. The investigations showed that a trivalent is formed at meiosis in the hybrid (2n = 65), segregation from which gives two classes of genetically balanced spermatozoa. Both of these are capable of producing normal offspring if they fertilize the eggs of a domestic mare.
Publication Date: 1975-10-01 PubMed ID: 1060807
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  • Journal Article

Summary

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This research article presents the detailed studies of testicular meiosis in three different horse hybrids, ultimately noting varying results depending upon the specific hybrid, with most notable abnormalities in the mule and hinny, but regular spermatogenesis in the Przewalski horse/domestic horse hybrid.

Overview of the Study

  • The study examined testicular meiosis, a division of male germ cells, in three different equine hybrids: mule, hinny, and a hybrid of Przewalski horse and domestic horse.
  • It primarily focused on the pachytene stage of meiotic prophase – a crucial step in meiosis where homologous chromosomes pair up and exchange genetic material.

Findings in Mule and Hinny

  • For the mule and hinny, the researchers observed abnormalities during most germ cells’ pairing at the pachytene stage.
  • Additionally, spermatogenesis, the process of sperm cell development, was almost completely halted in these two hybrids.
  • Nevertheless, a small number of mature spermatozoa were found in both the ejaculate and epididymal flushings of the hinny. This suggests that while meiosis is disrupted, it’s not entirely prevented.

Findings in Przewalski Horse/Domestic Horse Hybrid

  • In contrast, the hybrid of the Przewalski horse (Equus przewalskii) and domestic horse (E. caballus) showed normal spermatogenesis, indicating a successful meiotic process.
  • Banding studies of chromosomes showed a close kinship between the chromosomes of the Przewalski horse (with 66 chromosomes) and the domestic horse (with 64 chromosomes).
  • The researchers inferred that a Robertsonian translocation occurred, transforming four of E. przewalskii’s acrocentric chromosomes into two metacentric chromosomes of E. caballus. This chromosomal event may be why this hybrid horse can undergo normal spermatogenesis.

Implications of the Results

  • Due to the trivalent that is formed at meiosis in the Przewalski horse/domestic horse hybrid (with 65 chromosomes), two types of genetically balanced spermatozoa are created, both capable of fertilizing the eggs of a domestic mare and leading to regular offspring.
  • The study offers critical insights into equine hybrid fertility and the biological mechanisms that underpin it, which can impact breeding efforts in the future.

Cite This Article

APA
Chandley AC, Short RV, Allen WR. (1975). Cytogenetic studies of three equine hybrids. J Reprod Fertil Suppl(23), 356-370.

Publication

ISSN: 0449-3087
NlmUniqueID: 0225652
Country: England
Language: English
Issue: 23
Pages: 356-370

Researcher Affiliations

Chandley, A C
    Short, R V
      Allen, W R

        MeSH Terms

        • Animals
        • Cytogenetics
        • Horses
        • Hybridization, Genetic
        • Karyotyping
        • Male
        • Meiosis
        • Perissodactyla / physiology
        • Spermatogenesis

        Citations

        This article has been cited 7 times.
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        4. Bikchurina TI, Tishakova KV, Kizilova EA, Romanenko SA, Serdyukova NA, Torgasheva AA, Borodin PM. Chromosome Synapsis and Recombination in Male-Sterile and Female-Fertile Interspecies Hybrids of the Dwarf Hamsters (Phodopus, Cricetidae). Genes (Basel) 2018 Apr 25;9(5).
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          doi: 10.1534/genetics.118.300777pubmed: 29610216google scholar: lookup
        6. Torgasheva AA, Borodin PM. Cytological basis of sterility in male and female hybrids between sibling species of grey voles Microtus arvalis and M. levis. Sci Rep 2016 Nov 4;6:36564.
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        7. Han H, Wang A, Liu L, Zhao G, Su J, Wang B, Li Y, Zhang J, Wu B, Sun W, Hu S, Li S, Zhao L, Li X. Testicular Characteristics and the Block to Spermatogenesis in Mature Hinny. Asian-Australas J Anim Sci 2016 Jun;29(6):793-800.
          doi: 10.5713/ajas.15.0670pubmed: 26954128google scholar: lookup