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. Typically, prior to an asexual division, a cell duplicates its genetic information content, and then divides. The male parts of the flower are the stamens: These fungi are typically isogamous , lacking male and female specialization: Environmental sex determination For many species, sex is not determined by inherited traits, but instead by environmental factors experienced during development or later in life.
Other examples demonstrate that it is the preference of females that drive sexual dimorphism, such as in the case of the stalk-eyed fly. 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. Chromosomes are passed on from one generation to the next in this process. Sexual reproduction first probably evolved about a billion years ago within ancestral single-celled eukaryotes. Sex-determination system Sex helps the spread of advantageous traits through recombination. 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. Overview The male gamete sperm fertilizing the female gamete ovum One of the basic properties of life is reproduction, the capacity to generate new individuals, and sex is an aspect of this process. These fungi are typically isogamous , lacking male and female specialization: Female left and male right cones are the sex organs of pines and other conifers. Thus, XX mammals are female and XY are male. The ZW sex-determination system is shared by birds, some fish and some crustaceans. This mode of reproduction is called asexual, and it is still used by many species, particularly unicellular, but it is also very common in multicellular organisms, including many of those with sexual reproduction. Many reptiles have temperature-dependent sex determination: The majority of butterflies and moths also have a ZW sex-determination system. However, no third gamete type is known in multicellular plants or animals. In most birds, both excretion and reproduction is done through a single posterior opening, called the cloaca —male and female birds touch cloaca to transfer sperm, a process called "cloacal kissing". 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. Exceptions are common—for example, the roundworm C. A isogamy of motile cells , B isogamy of non-motile cells, C conjugation. 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. This is called X0 sex-determination —the 0 indicates the absence of the sex chromosome. Many fish change sex over the course of their lifespan, a phenomenon called sequential hermaphroditism. The penis contains a tube through which semen a fluid containing sperm travels. Male cones are smaller and produce pollen which is transported by wind to land in female cones. Flowers are usually hermaphroditic, producing both male and female gametes. Because of their motility, animal sexual behavior can involve coercive sex. The resulting cells are called gametes , and contain only half the genetic material of the parent cells.
Video about sex with a male friend:
The Truth About Women and their "Male Friends"!
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