Which of the following can be used to cut dna so it can be studied?
a. restriction enzymes
b. gel electrophoresis
c. karyotypes
d. haplotypes

The best answer is A.

A restriction enzyme is an enzyme that catalyzes the cleavage of DNA after recognizing a specific sequence of DNA.

Restriction enzymes are proteins produced by bacteria that cut  DNA at specific sites. These enzymes are used by bacteria to defend against bacterial viruses known as bacteriophages.  When a phage infects a bacteria, it inserts  its DNA into the bacteria so as to be replicated.

The restriction enzyme thwarts the replication of the phage DNA  by cutting it into many pieces. These enzymes  have been isolated from bacteria by scientists and used as indispensable tools in recombinant DNA technology.

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.