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 and When to Go. Pennsylvania weather essentials. The weather in Pennsylvania varies from place to place. Overall, however, it is the same as the rest of the northeastern United States, with four very distinct seasons. Spring and fall are typically mild and pleasant, with temperatures ranging anywhere from 55 to 75 degrees Fahrenheit.