Specialising in a field during a PhD at the expense of forgetting other areas I'm having a crisis of confidence: I'm a 3rd year PhD focusing on cancer genetics. Whilst I am undoubtedly developing a deep and broad understanding of genetics, bioinformatics, somatic evolution...all that good stuff; I'm also finding that my understanding of basics is all but disappearing. 

I don't use or "need" (practically speaking) a working knowledge of biochemistry or molecular biology to answer my research questions. Whilst during my undergrad I could describe cellular processes like translation, splicing, various cell signalling cascades in detail, I can barely summon the basics anymore. Since genetics, biochemistry, and molecular biology are so intimately related, I feel like drilling deep into one at the expense of the others is bad.

Is this something that other people experience? How do you find time to refresh the knowledge of areas that you 'should' know, even if you have no use for them anymore in your research?
Is this something that other people experience?


Yes, this is completely normal. Our memories get hazier over time, particularly if we don't make use of them. It is nothing to be worried about. We can't keep everything fresh in our minds at all times - as you learn new things, older topics get pushed to the sidelines and we may lose some of the detail. 

However, memory is a complicated phenomenon, and just because you are having trouble accessing a memory doesn't mean that it's been completely overwritten. As @PatricianShanahan hints in a comment, I suspect you would find that if you had to re-learn some of these topics, it would come back to you surprisingly quickly. Partly because the memories are still hidden away somewhere, and partly because you will have been getting better and better at the process of learning itself.


  How do you find time to refresh the knowledge of areas that you 'should' know, even if you have no use for them anymore in your research? 


I don't think there is any particular need to force this process. The memories that fade the most are the ones that are being used the least, and there's a good reason for that: they are the ones that are less important to you. 

General reading will help to keep memories fresh - it's always useful to read broadly around your subject. If you are worried about forgetting things because they are interesting to you then try to find some enjoyable reading on the subject - perhaps pop-science books, or magazines.