**2.3 Thyrotropin alpha subunit gene (***CGA***)**

Thyrotropin is a member of the glycoprotein hormone family which consisting thyrotrophin, follicle-stimulating hormone and luteinizing hormone in anterior pituitary, and chorionic gonadotrophin in the placenta. Each of these hormones is a heterodimer composed of a common α subunit and a hormone specific β subunit. The common α subunit is encoded by the *CGA* gene, while the TSH specific β subunit is encoded by the *TSHB* gene.

Porcine *CGA* gene is 14 kb in length and consists of four exons and three introns (Kato et al., 1991). The coding region starts from the exon 2, and the premature peptide contains a signal peptide of 24 amino acids. Two intragenic microsatellites were found in intron 1 and intron 2. The microsatellite located in the intron 1 has been named as PGHAS or ALPHA and widely used in genetic studies as genetic marker.
