GAPDH as a control gene to estimate genome copy number in Great Tits, with cross-amplification in Blue Tits

Estimating the number of genome copies in a tissue sample can serve various purposes. For example, such an estimate serves as a scaling variable when measuring telomeres with quantitative PCR. We describe the primer development and evaluation for the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene in the Great Tit Parus major, as a control gene to estimate genome copy number. We demonstrate specific amplification with negligible variation in 48 Great Tits and cross-amplification in 53 Blue Tits Cyanistes caeruleus. We conclude this primer set to be reliable for amplification of GAPDH as a reference gene for quantitative PCR analysis in Great and Blue Tits.