The correct combination is (1) A and B.

• Copy number of integrated transgene is determined at the DNA level.

• Tissue‑specific transcription is assessed at the RNA level.

Using that logic:

Role of each technique

A. Polymerase Chain Reaction (PCR) – relevant for copy number

• Genomic PCR (especially quantitative or digital PCR) can estimate transgene copy number relative to a reference gene.

• It works on DNA, so it directly reflects how many copies of the transgene are integrated.

B. Southern blot hybridization – classical copy-number method

• Southern blot on genomic DNA is the traditional, gold-standard method to determine number and arrangement of integrated copies of a transgene.

• Band number/intensity reveals copy number and sometimes insertion pattern.

Together, A and B are appropriate for the “location/number integrated into genome” part of the question.

C. Reverse Transcriptase PCR – tissue-specific transcription, not copy number

• RT‑PCR starts from RNA, so it measures mRNA levels and tissue‑specific expression.

• It does not tell you how many copies of the gene are integrated; different copy numbers can give similar or different RT‑PCR signals depending on regulation.

D. Western blot – protein level, not copy number or transcription

• Western blot detects protein, so it reports translation level and post‑translational stability, not DNA copy number.

• Protein can be absent despite transcription (post‑transcriptional control), so it is not a direct measure of tissue‑specific transcription either.

Why option (1) is correct

For the problem as framed—“determine the copy number of genes and their tissue‑specific transcription”—the combination that covers copy number (PCR/Southern) plus allows inference about transcription (PCR-based assays using cDNA) is best represented by A and B, whereas C (RT‑PCR) focuses only on RNA and D (Western) only on protein.