A parent DNA molecule with both strands labeled with light nitrogen (${}^{14}N$) is transferred to a growth medium containing only heavy nitrogen (${}^{15}N$) and allowed to undergo four rounds of replication.

Which of the following statements correctly predict the results if DNA replication is semiconservative?

1. After three rounds of replication, 75% of the double-stranded DNA molecules are of heavy density (${}^{15}N{/}^{15}N$).
2. After four rounds of replication, the ratio of hybrid-density (${}^{14}N{/}^{15}N$) to heavy-density (${}^{15}N{/}^{15}N$) DNA molecules is $1:8$.
3. After three rounds of replication, 12.5% of the individual polynucleotide strands in the population contain ${}^{14}N$.