In pines and other conifers the sex organs are conifer cones and have male and female forms. The ZW sex-determination system is shared by birds, some fish and some crustaceans. Plant reproduction Like animals, plants have developed specialized male and female gametes. Bacteria, for instance, reproduce asexually, but undergo a process by which a part of the genetic material of an individual donor is transferred to another recipient. In genetic sex-determination systems, an organism's sex is determined by the genome it inherits. In humans and other mammals this male organ is the penis , which enters the female reproductive tract called the vagina to achieve insemination —a process called sexual intercourse. This sex-determination system results in highly biased sex ratios , as the sex of offspring is determined by fertilization rather than the assortment of chromosomes during meiosis. In sexual reproduction, there are special kinds of cells that divide without prior duplication of its genetic material, in a process named meiosis. Female left and male right cones are the sex organs of pines and other conifers.
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. Humans and other mammals have an XY sex-determination system: XY sex determination is used by most mammals,  but also some insects,  and plants Silene latifolia. The height of the mushroom aids the dispersal of these sexually produced offspring. Sexual dimorphisms in animals are often associated with sexual selection — the competition between individuals of one sex to mate with the opposite sex. In either case, gametes may be externally similar, particularly in size isogamy , or may have evolved an asymmetry such that the gametes are different in size and other aspects anisogamy. This double-chromosome stage is called " diploid ", while the single-chromosome stage is " haploid ". The male gamete, a spermatozoon produced in vertebrates within the testes , is a small cell containing a single long flagellum which propels it. In pines and other conifers the sex organs are conifer cones and have male and female forms. Exceptions are common—for example, the roundworm C. Sex differences in humans include, generally, a larger size and more body hair in men; women have breasts, wider hips, and a higher body fat percentage. Isogamy and Anisogamy The life cycle of sexually reproducing organisms cycles through haploid and diploid stages Sexual reproduction in eukaryotes is a process whereby organisms form offspring that combine genetic traits from both parents. These fungi are typically isogamous , lacking male and female specialization: The male parts of the flower are the stamens: Other examples demonstrate that it is the preference of females that drive sexual dimorphism, such as in the case of the stalk-eyed fly. Evolution of sexual reproduction Different forms of anisogamy: Sometimes intersex individuals are called "hermaphrodite"; but, unlike biological hermaphrodites, intersex individuals are unusual cases and are not typically fertile in both male and female aspects. In many organisms, the haploid stage has been reduced to just gametes specialized to recombine and form a new diploid organism; in others, such as cryptogamic plants the gametes are capable of undergoing cell division to produce multicellular haploid organisms. A isogamy of motile cells , B isogamy of non-motile cells, C conjugation. Humans and other mammals have an XY sex-determination system: This process of cell division is called mitosis. Animals which live in the water can mate using external fertilization , where the eggs and sperm are released into and combine within the surrounding water. Traumatic insemination , for example, is used by some insect species to inseminate females through a wound in the abdominal cavity—a process detrimental to the female's health. In some of these cases, the fusion is asymmetric, and the cell which donates only a nucleus and not accompanying cellular material could arguably be considered "male". Genetic sex-determination usually depends on asymmetrically inherited sex chromosomes which carry genetic features that influence development ; sex may be determined either by the presence of a sex chromosome or by how many the organism has.
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Sex Is Zero 1 (2011)
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