What is the expected probe size to target a single site in the human haploid genome?

The correct answer reflects the necessity for a probe to be of sufficient length to uniquely hybridize to a specific target site within the human haploid genome, which contains approximately 3 billion base pairs. A probe of 16 base pairs is often considered the minimal length needed to achieve a reliable level of specificity for hybridization.

In molecular biology, the likelihood of random binding increases with shorter probes. Probes that are too short (like those of 6 or 10 base pairs) may bind non-specifically to multiple sites due to the vast number of similar sequences scattered throughout the genome. A probe of 16 base pairs strikes a balance between specificity and the ability to efficiently hybridize to its target sequence.

Furthermore, probes longer than 16 base pairs, such as those that are 26 base pairs, are indeed more specific but may also require more stringent conditions for hybridization and could result in higher costs and extended development times for probe synthesis. Therefore, while longer probes provide increased specificity, 16 base pairs is generally optimal for targeting single sites in terms of practicality and effectiveness, making it the expected size for this purpose.