A gene called ________ is linked to increasing presence of plaques and tangles in the brain.

Many individuals decide that they feel hungry and eat lunch when they see both hands of the clock on the 12, indicating that it is noontime. This may occur regardless of how recently they ate breakfast. In this example, the conditioned stimulus is the____

a. food they eat for lunch; eating lunch b. number of hours since breakfast; watching the hands of the clock c. act of eating lunch; watching the hands of the clock d. hands of the clock; eating lunch

Which of the following is NOT one of the nucleotide base molecules that form DNA?

A) xanthine B) thymine C) guanine D) cytosine