Comparative chromosomal studies of E. caballus (ECA) and E. przewalskii (EPR) in a female F1 hybrid.

The study compared chromosomal characteristics of two horse species, Equus caballus (2n = 64) and Equus przewalskii (2n = 66), focusing primarily on their differences in specific chromosome pairs. The researchers found that the chromosome ECA 5 in Equus caballus corresponds to two chromosomal pairs in Equus przewalskii, EPR 23 and EPR 24, suggesting a Robertsonian translocation event.

Background of the Research

• The study was conducted to provide a deeper understanding of the chromosomal differences between the two species of horses – Equus caballus (ECA) and Equus przewalskii (EPR).
• Previous studies had revealed that Equus przewalskii (2n = 66) and Equus caballus (2n = 64) differ by one pair of metacentric chromosomes, present in ECA but not in EPR.
• Another two pairs of acrocentric chromosomes are found only in the EPR karyotype.
• Therefore, the researchers examined the formation of a trivalent during meiosis in a male F1 hybrid, an occurrence suggesting that ECA 5 corresponds to two acrocentric EPR chromosomes, implying a Robertsonian fusion or fission event.

Methodology

• The researchers carried out chromosomal investigations of a female interspecies F1 hybrid, deploying tools such as banded karyograms and fluorescence in situ hybridization (FISH) studies to focus on the p and q arm of ECA 5.
• They examined Q- and G-banding patterns of E. caballus, E. przewalskii and the hybrid to identify homology between all chromosome pairs.

Findings

• The study recognized interspecies homology between all chromosome pairs except for ECA 5, EPR 23 and EPR 24, each unique for a particular species.
• The findings exhibited homology between ECA 5p and EPR 23, and between ECA 5q and EPR 24.
• FISH revealed hybridization of the BACs laminin beta 3 (LAM B3) and laminin gamma 2 (LAM C2) to ECA 5p and EPR 23.
• Contrastingly, nuclear factor I (NFIA) and immunoglobulin lambda (IGL@), primarily assigned to ECA 5q, were mapped to ECA 7 and EPR 6 respectively.
• This indicates the karyotypes of E. caballus and E. przewalskii are different, with the variance attributed to a single Robertsonian translocation event (where ECA 5 equals EPR 23 and EPR 24).