<P> Some species that are capable of reproducing asexually, like hydra, yeast (See Mating of yeasts) and jellyfish, may also reproduce sexually . For instance, most plants are capable of vegetative reproduction--reproduction without seeds or spores--but can also reproduce sexually . Likewise, bacteria may exchange genetic information by conjugation . </P> <P> Other ways of asexual reproduction include parthenogenesis, fragmentation and spore formation that involves only mitosis . Parthenogenesis is the growth and development of embryo or seed without fertilization by a male . Parthenogenesis occurs naturally in some species, including lower plants (where it is called apomixis), invertebrates (e.g. water fleas, aphids, some bees and parasitic wasps), and vertebrates (e.g. some reptiles, fish, and, very rarely, birds and sharks). It is sometimes also used to describe reproduction modes in hermaphroditic species which can self - fertilize . </P> <P> Sexual reproduction is a biological process that creates a new organism by combining the genetic material of two organisms in a process that starts with meiosis, a specialized type of cell division . Each of two parent organisms contributes half of the offspring's genetic makeup by creating haploid gametes . Most organisms form two different types of gametes . In these anisogamous species, the two sexes are referred to as male (producing sperm or microspores) and female (producing ova or megaspores). In isogamous species, the gametes are similar or identical in form (isogametes), but may have separable properties and then may be given other different names (see isogamy). For example, in the green alga, Chlamydomonas reinhardtii, there are so - called "plus" and "minus" gametes . A few types of organisms, such as many fungi and the ciliate Paramecium aurelia, have more than two "sexes", called syngens . Most animals (including humans) and plants reproduce sexually . Sexually reproducing organisms have different sets of genes for every trait (called alleles). Offspring inherit one allele for each trait from each parent . Thus, offspring have a combination of the parents' genes . It is believed that "the masking of deleterious alleles favors the evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases" where recombination occurs freely . </P> <P> Bryophytes reproduce sexually, but the larger and commonly - seen organisms are haploid and produce gametes . The gametes fuse to form a zygote which develops into a sporangium, which in turn produces haploid spores . The diploid stage is relatively small and short - lived compared to the haploid stage, i.e. haploid dominance . The advantage of diploidy, heterosis, only exists in the diploid life generation . Bryophytes retain sexual reproduction despite the fact that the haploid stage does not benefit from heterosis . This may be an indication that the sexual reproduction has advantages other than heterosis, such as genetic recombination between members of the species, allowing the expression of a wider range of traits and thus making the population more able to survive environmental variation . </P>

Any cell of a living organism other than the reproductive cells