In many cases the male of a species is larger than the female. In field cricketsfor example, insects with a single X chromosome develop as male, while those with two develop as female. Mosses of Eastern North America. Humans and other mammals have an XY sex-determination system: One of many books by this pioneering authority on aspects of human sexuality.
When a pollen grain lands upon the stigma on top of a carpel's style, it germinates to produce a pollen tube that grows down through the tissues of the style into the carpel, where it delivers male gamete nuclei to fertilize an ovule that eventually develops into a seed.
Sexual reproduction is a process specific to eukaryotesorganisms whose cells contain a nucleus and mitochondria. Play games, ask experts questions, talk to other girls, and learn the facts about what's going on in your life all on Gurl. Avatars by Sterling Adventures. In both XY and ZW sex determination systems, the sex chromosome carrying the critical factors is often significantly smaller, carrying little more than the genes necessary for triggering the development of a given sex. As sexual reproduction developed by way of a long process of evolution, intermediates exist.