and, in case you thought this wasn't relevant to today's lecture:
The Footprints of Winter - Epigenetic marks laid down during the cold months of the year allow flowering in spring and summer.
Many plants that grow in climates with a cold winter require growth for several months at low temperatures—a process called vernalization—to promote flowering in spring, when days lengthen and temperatures increase. Without this period of cold, plants would grow leaves in the spring, but would fail to flower. This phenomenon, familiar to every horticulturist, was difficult to explain with genetics alone; something occurred during those cold months that left a mark, which, in effect, released a switch that permitted flowering in spring. In recent years, the field has looked beyond the genome and found that vernalization is controlled by a wide range of epigenetic mechanisms.