Analyzing the bottleneck faced by a Scrum team, Mark Levison introduces in this blog post the concept of Skills Matrix. The Skill Matrix is a visual management tool that shows at a glance how much cross-training you have in your organization between different people and different tasks.
You will be able to spot the areas where you have one person who could do the work, which is often what will cause bottlenecks in the first place. To improve the skills gaps, Mark Levison suggests a mixture of pair programming, interactive workshops and one on one coaching. These activities might initially slow the team down, but it will bring the benefits of getting higher priority work done faster in the future.