The study was conducted on fertilized eggs from Broiler chickens of the fast-growing strain Ross 308. The eggs were split into two experimental conditions: incubation in normoxia (21 % O₂) and in chronic isobaric hypoxia (14 % O₂). Embryos were sampled at two developmental ages: 15 days and 19 days of a total of 21 days of incubation.

Giving a total of four experimental groups, each having a total sample size of eight embryos (n=8):

15 days Normoxic (15N)

15 days Hypoxic (15H)

19 days Normoxic (19N)

19 days Hypoxic (19H)

With the first strand cDNA synthesized from the extracted mRNA from the 15 day and 19 day embryonic chicken cardiac tissue samples, qPCR analysis of the β₁AR, β₂AR and housekeeper gene, GAPDH, mRNA expression levels was performed. The difference in mRNA expression of each gene was evaluated, normalized by the reference gene GAPDH from the qPCR results obtained using Rotor-Gene^™ 6000 software. The calculated concentrations of the control (normoxic) and the test (hypoxic) samples was used to determine if there is a difference in the relative expression ratio in mRNA expression normalized by the reference gene (GAPDH) with respect to different treatment conditions or age.