Unveiling genetic diversity in Egyptian Arabian horses (Equus caballus) through cytogenetic and ISSR marker analysis.

Overview

• This research analyzed genetic diversity in Egyptian Arabian horses by combining classical chromosome analysis (cytogenetics) with molecular marker techniques (ISSR markers).
• The study confirms chromosome stability in these horses and reveals moderate genetic diversity using ISSR markers, which can support conservation and breeding efforts.

Introduction and Objectives

• The goal was to assess the genetic diversity of Egyptian Arabian horses, a valuable and historically significant breed.
• Two main methods were used: cytogenetics (to examine chromosomes visually) and ISSR (Inter Simple Sequence Repeat) markers (to analyze DNA variation).
• Understanding genetic diversity helps in ensuring healthy breeding programs and conserving genetic resources.

Cytogenetic Analysis

• Karyotyping was performed on 24 Egyptian Arabian horses to study their chromosomes.
• The standard number of chromosomes (2n = 64) was confirmed, meaning all horses had the typical equine chromosome count with no visible abnormalities.
• Chromosome morphology matched international standards (ISCN Equine), ensuring the chromosomes’ relative lengths and centromere positions are as expected:
• Autosomal chromosomes’ relative lengths (RL%) followed a typical size order.
• Biarmed chromosomes demonstrated metacentric to submetacentric forms with centromeric index (CI) ranging between 37-50%.
• All acrocentric chromosomes had measurable p-arms, based on recalculated centromeric indices.

ISSR Marker Analysis

• DNA from the horses was analyzed using 9 ISSR primers, generating 117 DNA bands for genetic comparison.
• Of these bands, 104 (about 88.89%) were polymorphic, indicating genetic variation among individuals.
• Two primers, (AGC)₆G and (GAG)₆C, were particularly informative, showing very high polymorphism rates of 95.24% and 93.75%, respectively.
• The high polymorphism suggests these primers cover a broad portion of the horse genome and are useful for diversity studies.

Genetic Diversity Metrics

• Three key parameters were calculated:
• P% (percentage of polymorphic loci): 88.89%, indicating a large proportion of variable DNA regions.
• H (Nei’s gene diversity index): 0.32, showing moderate diversity.
• I (Shannon’s information index): 0.48, reflecting diverse genetic information content.
• Pairwise Dice similarity coefficients, ranging from 0.70 to 0.98, revealed moderate to high genetic relatedness among individual horses.
• However, no distinct genetic subgroups within the sampled population were detected, suggesting a relatively homogeneous gene pool.

Conclusions and Implications

• The study confirmed that Egyptian Arabian horses have stable chromosomes with no detectable abnormalities, reinforcing breed health.
• ISSR markers proved to be effective in detecting moderate genetic diversity and relationship patterns within the breed.
• These findings serve as a foundational baseline for future research, including more extensive genomic studies and conservation genetics.
• The results can guide breeding programs aimed at maintaining or enhancing genetic diversity to ensure the breed’s vitality and sustainability.