Final answer:
A Tm difference of 5 or more between primers can lead to decreased product yield in PCR.
Step-by-step explanation:
When designing primers for PCR, it is important for the melting temperatures (Tm) of the primers to closely match. A Tm difference of 5 or more can lead to decreased product yield. The melting temperature is the temperature at which the double-stranded DNA separates into single strands. If the Tm difference is too large, one primer may denature while the other remains hybridized to the template, resulting in incomplete or no amplification.