II. Reconstruct the following text using the words from the box to fill in the blanks. What do you think about extraterrestrial life?
cycles
strands
primers
copies
diseases
nucleotides
deoxyribonucleic acid
test
complementary
enzyme
blood
piece
fragment
segment
technique
round
tube
duplicated
amplify
replicated
multiplied
research
identify
heating
sufficient
Polymerase Chain Reaction (PCR) is a (1)_________ in molecular biology by which a small fragment of (2)_________ can be rapidly cloned, or (3)_________, to produce multiple DNA (4)_________. PCR can be used to (5)_________ individuals from minute amounts of tissue or (6)_________, to diagnose genetic (7)_________, and to (8)_________ evolution.
PCR proceeds in a series of (9)_________, or rounds. Each successive (10)_________ doubles the amount of DNA and thus more than 1 billion copies of a single DNA (11)_________ can be made in just a few hours. Performed in a test (12)_________, PCR mirrors the way in which DNA is (13)_________ within a cell. To perform PCR, scientists isolate the piece of DNA to be amplified ((14)_________) in a test tube and heat it to separate the two (15)_________ of the molecule. As cooling occurs, short pieces of DNA called (16)_________ are added to the test tube. The primers attach to each strand, marking the (17)_________ that will be cloned. Free-floating nucleotides and an (18)_________ called DNA polymerase are then added to the mixture. DNA polymerase uses the free-floating (19)_________ to build a (20)_________ copy of each amplified DNA segment, resulting in two new double-stranded DNA molecules. Each cycle of (21)_________ and cooling doubles the amount of the desired DNA fragment in the (22)_________ tube. In a matter of hours, scientists can obtain millions of copies of a desired (23)_________ of DNA. PCR enables scientists to (24)_________ traces of DNA found at a crime scene or in a fossil animal to produce (25)_________ quantities to study.