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Males
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs. Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically; however, species such as ''Cymothoa exigua'' change sex depending on the number of females present in the vicinity. In humans, the word ''male'' can also be used to refer to gender in the social sense of gender role or gender identity. Overview The existence of separate sexes has evolved independently at different times and in different lineages, an example ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sexual Dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most animals and some plants. Differences may include secondary sex characteristics, size, weight, colour, markings, or behavioural or cognitive traits. These differences may be subtle or exaggerated and may be subjected to sexual selection and natural selection. The opposite of dimorphism is ''monomorphism'', which is when both biological sexes are phenotypically indistinguishable from each other. Overview Ornamentation and coloration Common and easily identified types of dimorphism consist of ornamentation and coloration, though not always apparent. A difference in coloration of sexes within a given species is called sexual dichromatism, which is commonly seen in many species of birds and reptiles. Sexual selection leads to the exaggerated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gender
Gender is the range of characteristics pertaining to femininity and masculinity and differentiating between them. Depending on the context, this may include sex-based social structures (i.e. gender roles) and gender identity. Most cultures use a gender binary, in which gender is divided into two categories, and people are considered part of one or the other ( boys/men and girls/ women);Kevin L. Nadal, ''The SAGE Encyclopedia of Psychology and Gender'' (2017, ), page 401: "Most cultures currently construct their societies based on the understanding of gender binary—the two gender categorizations (male and female). Such societies divide their population based on biological sex assigned to individuals at birth to begin the process of gender socialization." those who are outside these groups may fall under the umbrella term ''non-binary''. Some societies have specific genders besides "man" and "woman", such as the hijras of South Asia; these are often referred to as '' third g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sex-determination System
A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes. In some species there are hermaphrodites. There are also some species that are only one sex due to parthenogenesis, the act of a female reproducing without fertilization. In some species, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. In animals this is often accompanied by chromosomal differences, generally through combinations of XY, ZW, XO, ZO chromosomes, or haplodiploidy. The sexual differentiation is generally triggered by a main gene (a "sex locus"), with a multitude of other genes following in a domino effect. In other cases, sex of a fetus is determined by environmental variables (such as temperature). The details of some sex-determination systems are not yet fully under ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Testosterone
Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair. In addition, testosterone in both sexes is involved in health and well-being, including moods, behaviour, and in the prevention of osteoporosis. Insufficient levels of testosterone in men may lead to abnormalities including frailty and bone loss. Testosterone is a steroid from the androstane class containing a ketone and a hydroxyl group at positions three and seventeen respectively. It is biosynthesized in several steps from cholesterol and is converted in the liver to inactive metabolites. It exerts its action through binding to and activation of the androgen receptor. In humans and most other vertebrates, testosterone is secreted primarily by the testicles of m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Y Chromosome
The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the gene SRY, which triggers male development. The DNA in the human Y chromosome is composed of about 59 million base pairs, making it similar in size to chromosome 19. The Y chromosome is passed only from father to son. With a 30% difference between humans and chimpanzees, the Y chromosome is one of the fastest-evolving parts of the human genome. The human Y chromosome carries an estimated 100–200 genes, with between 45 and 73 of these being protein-coding. All single-copy Y-linked genes are hemizygous (present on only one chromosome) except in cases of aneuploidy such as XYY syndrome or XXYY syndrome. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cymothoa Exigua
''Cymothoa exigua'', or the tongue-eating louse, is a parasitic isopod of the family Cymothoidae. It enters fish through the gills. The female attaches to the tongue, while the male attaches to the gill arches beneath and behind the female. Females are long and wide. Males are about long and wide. The parasite severs the blood vessels in the fish's tongue, causing the tongue to fall off. It then attaches itself to the remaining stub of tongue and the parasite itself effectively serves as the fish's new "tongue". Behavior Using its front claws, ''C. exigua'' severs the blood vessels in the fish's tongue, causing the tongue to necrose from lack of blood. The parasite then replaces the fish's tongue by attaching its own body to the muscles of the tongue stub. The parasite apparently does not cause much other damage to the host fish, but Lanzing and O'Connor (1975) reported that infested fish with two or more of the parasites are usually underweight. Once ''C. exigua'' repl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Female
Female ( symbol: ♀) is the sex of an organism that produces the large non-motile ova (egg cells), the type of gamete (sex cell) that fuses with the male gamete during sexual reproduction. A female has larger gametes than a male. Females and males are results of the anisogamous reproduction system, wherein gametes are of different sizes, unlike isogamy where they are the same size. The exact mechanism of female gamete evolution remains unknown. In species that have males and females, sex-determination may be based on either sex chromosomes, or environmental conditions. Most female mammals, including female humans, have two X chromosomes. Female characteristics vary between different species with some species having pronounced secondary female sex characteristics, such as the presence of pronounced mammary glands in mammals. In humans, the word ''female'' can also be used to refer to gender in the social sense of gender role or gender identity. Etymology and usage ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fertilization
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Processes such as insemination or pollination which happen before the fusion of gametes are also sometimes informally called fertilisation. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation. History In Antiquity, Aristotle conceived the formation of new individuals through fusion of male and female fluids, with form and function emerging gradually, in a mode called by him as epigenetic. In 1784, Spallanzani established the need of interaction between the female's ovum and male's sperm to form a zygote in fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homo Sapiens
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, and language. Humans are highly social and tend to live in complex social structures composed of many cooperating and competing groups, from families and kinship networks to political states. Social interactions between humans have established a wide variety of values, social norms, and rituals, which bolster human society. Its intelligence and its desire to understand and influence the environment and to explain and manipulate phenomena have motivated humanity's development of science, philosophy, mythology, religion, and other fields of study. Although some scientists equate the term ''humans'' with all members of the genus ''Homo'', in common usage, it generally refers to ''Homo sapiens'', the only extant member. Anatomically mod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles (including birds) from which they diverged in the Carboniferous, over 300 million years ago. Around 6,400 extant species of mammals have been described divided into 29 orders. The largest orders, in terms of number of species, are the rodents, bats, and Eulipotyphla ( hedgehogs, moles, shrews, and others). The next three are the Primates (including humans, apes, monkeys, and others), the Artiodactyla (cetaceans and even-toed ungulates), and the Carnivora ( cats, dogs, seals, and others). In terms of cladistics, which reflects evolutionary history, mammals are the only living members of the Synapsida (synapsids); this clade, toget ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anisogamy
Different forms of anisogamy: A) anisogamy of motile cells, B) egg_cell.html"_;"title="oogamy_(egg_cell">oogamy_(egg_cell_and_sperm_cell),_C)_anisogamy_of_non-motile_cells_(egg_cell_and_spermatia)..html" ;"title="egg_cell_and_sperm_cell.html" ;"title="egg_cell.html" ;"title="oogamy (egg cell">oogamy (egg cell and sperm cell">egg_cell.html" ;"title="oogamy (egg cell">oogamy (egg cell and sperm cell), C) anisogamy of non-motile cells (egg cell and spermatia).">283x283px Anisogamy is a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form. The smaller gamete is male, a sperm cell, whereas the larger gamete is female, typically an [gg cell. Anisogamy is predominant among multicellular organisms. In both plants and animals gamete size difference is the fundamental difference between females and males. Anisogamy most likely evolved from isogamy. Since the biological definition of male and female is based on gamete size, th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oogamy
Oogamy is an extreme form of anisogamy where the gametes differ in both size and form. In oogamy the large female gamete (also known as ovum) is immobile, while the small male gamete (also known as sperm) is mobile. Oogamy is a common form of anisogamy, with almost all animals and land plants being oogamous. Occurrence Oogamy is found in most species that reproduce sexually, all higher species being oogamous. Oogamy is found in all land plants, and in some red algae, brown algae and green algae. Oogamy is favored in plants because only one gamete has to travel through harsh environments outside the plant. Oogamy is also present in oomycetes. Almost all animals are oogamous. There are exceptions, such as the opiliones that have immobile sperm. Etymology The term oogamy was first used in the year 1888. Evolution It is generally accepted that isogamy is the ancestral state and that oogamy evolves from isogamy through anisogamy. However, transitions do exist between a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
