The use of restriction enzymes as a way to cut DNA molecules was first demonstrated in a classic study by Johns Hopkins biochemist Daniel Nathans and his graduate student Kathleen Danna (Danna & Nathans, 1971).
Home : Climate Graphs: Pennsylvania : Philadelphia. Philadelphia's coldest month is January when the average temperature overnight is 25.5Â°F. In July, the warmest month, the average day time temperature rises to 85.5Â°F.
Pennsylvania Weather Climate: Like all mountainous states, the four seasons differ in intensity based on your location. Pennsylvania summers are long, bringing hot and humid conditions to the southeast, while in the mountains (central, northeast and west) the days are generally cooler, but still on the humid side. Fall is pleasant throughout the state, while winter brings snow and much colder temperatures.