Molecular and cytogenetic studies in a case of XX SRY-negative sex reversal in an Arabian horse.

The abstract discusses a study on a 18-month old Arabian foal with both male and female physical characteristics. The study uses molecular and cytogenetic analysis to understand the genetic basis of this sex reversal, revealing a normal female genome but a lack of SRY and ZFY genes typically related to male hormones.

Cytogenetic and Molecular Genetic Examination

• The research focuses on an Arabian foal which had physical attributes of a stallion, but also displayed abnormalities in its external genitalia along with the presence of ovotestis-like structures in its abdomen.
• The researchers carried out cytogenetic and molecular genetic examinations on the foal. Cytogenetic research focuses on the structure and number of chromosomes, and in genetics, the term ‘molecular’ refers to the study of genes and their function at a molecular level.

Findings Through RB-Banding

• RB-banding (Reverse Banding) is a chromosome staining procedure that allows for the visualization and identification of structural abnormalities in chromosomes.
• The RB-banding revealed the foal to have a normal female equine (horse) karyotype of 2n=64,XX. A karyotype is the characterization of the chromosome complement of a species — in this case horse (2n=64,XX indicates it has 64 chromosomes and XX means it’s female).

Molecular Analysis Results

• The molecular analysis showed absence of the SRY (Sex-determining Region Y) and ZFY (Zinc finger protein on Y chromosome) genes, both of which are usually found in male animals.
• The ZFX (Zinc finger protein on X chromosome) gene, typically found in female horses, was present. The absence of male-associated genes and presence of the female-associated ZFX gene, despite the animal’s stallion-like traits, indicates a genetic female.

RSPO1 Coding Region Examination

• The researchers also examined the entire RSPO1 (R-Spondin1) coding region, a gene often linked with disorders of sex development, to determine if it had any role in the foal’s condition.
• Even though they found a single nucleotide polymorphism (SNP, a mutation or variation in a single DNA building block) in exon 3 of the RSPO1 gene, it did not cause an amino acid substitution, which mean it wasn’t responsible for changing the protein structure.