Handed down item old medics wrapped in shiny stuff (10)
I believe the answer is:
chromosome
'handed down item' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'old medics wrapped in shiny stuff' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'medics' becomes 'mos' (I can't explain this - if you can you should believe this answer much more).
'wrapped in' means one lot of letters goes inside another.
'shiny stuff' becomes 'chrome' (I've seen this before).
'o'+'mos'='omos'
'omos' going into 'chrome' is 'CHROMOSOME'.
Can you help me to learn more?
(Other definitions for chromosome that I've seen before include "Structure carrying genes" , "Gene carrier" , "structure in cell" , "Genetic structure" , "this could be X or Y" .)