During the 1900s, the following genetic discoveries were made: • DNA is the molecule responsible for inheritance.
• There are four bases in DNA, and they combine in a specific way. Adenine pairs with thymine, and guanine pairs with
cytosine.
• DNA is a double helix. The sugar molecules form the backbone, and the bases are connected by hydrogen bonds in the
middle.
• Enzymes that can cut and copy sections of DNA are identified and isolated.
As a result of these scientific discoveries, scientists are now able to

A.
determine some organisms' genetic sequences.
B.
change portions of genetic code to treat disease.
C.
clone certain organisms.
D.
all of these