An electrocardiogram, or ekg, is used to visualize what? electrical activity in the heart heart wall muscle movement heart valves blocked coronary arteries

The answer is electrical activity of the heart.  It illustrates the heart's electrical activity as line tracings on paper. The spikes and dips in the line tracings are called waves. during hospitalization, a sequence of EKGs are taken to monitor the ongoing changes which are indicative of a heart attack.

for the points

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).