The most common and most likely answer to this crossword clue is the 9 letter word GENOTYPES
I've seen this crossword clue in Financial Times
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Buddy explains!
The straight part
We know that "Biological groups" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case biological groups = genotypes.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GENOTYPES mean?
GENOTYPES noun- The part (DNA sequence) of the genetic makeup of an organism which determines a specific characteristic (phenotype) of that organism.
- A group of organisms having the same genetic constitution.
- To determine the genotype of.
- The type species of a genus; generitype.