Answer:
½ 15N-15N and ½ 14N-14N
Explanation:
The conservative model of replication is was postulated as the process in which an intact/whole double helix acts as a template for a newly synthesized double helix. According to Messelson-Stahl experiment, after the first round of replication, the parents strand which is the 15N-15N will act as a template to form the new strand which is the 14N-14N after taking up this form of nitrogen. Thus we have one whole double helix parental 15N-15N and one newly synthesized double helix 14N-14N. There would be no combination of the two.