Aperson can be tested for the allele that causes huntington’s disease because the of that allele is different from that of the normal allele.
a. dna sequence
b. alternative allele
c. size d.
protein structure

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A person can be tested for the allele that causes Huntington’s disease because the "DNA SEQUENCE," of that allele is different from that of the normal allele.

Hope this helps. ;)

Although i don't know what is the simulated system, starfish are predators that eat mostly  microalgae,  snails, sponges, bivalves, mussels and other small marine animals. removing starfish from any system would definitely increase this animals that they prey.

That is true it is called an aftershock