WAIT! WAIT! DON'T TELL ME! II

Three words have the consecutive letters LLEL:

PARALLEL

HALLELUJAH

What is the third word?

 

HINTS:

1. Six letters

2. The LLEL is in the middle

3. It's a scientific word, but not obscure

 

Answer:

 

The word is ALLELE - a variation of a gene on a chromosome