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what are some methods gymnosperms have of preventing self-fertilization  

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In gymnosperms, or cone-bearing plants, including Gingko, evergreens like pine trees and cycads, the sporophyte is the dominant generation. These plants can produce separate male and female cones containing modified leaves or sporophylls. Inside the sporophyll is the sporangium, which can form different sized male or female gametes called microspores and megaspores, respectively. The male cones are lower on the tree and on the sides, and the female cones are located higher. Since the male gametes are the pollen and are transferred by wind and the shape of this gamete is adapted for this, and because they are lower down, there is less chance for self-pollination. Instead,  cross-pollination between two different plants is generally what occurs. This leads to more genetic variation when sexual reproduction occurs between two different individuals.

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