How do gynoecious cucumber varieties differ from other varieties?

Cucumbers and other vine crops are monoecious.  Monoecious plants have separate male and female flowers on the same plant.  Male and female flowers are similar in appearance.  However, the female flowers have small, immature fruits at their base.  Pollen is transferred from the male to the female flowers by bees and other pollinators.  When properly pollinated and fertilized, the female flowers develop into fruit.  The first flowers to appear on cucumbers and other vine crops are usually male.  Female flowers appear shortly thereafter. 

Gynoecious varieties are special hybrids which produce predominantly female flowers.  Seeds of a standard monoecious variety are commonly included in the seed packet to ensure adequate pollination.  (The seeds of the monoecious variety may be dyed or placed in a separate packet.)  Gynoecious varieties often outproduce standard varieties when a pollenizer (monoecious variety) is present.