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The XO sex-determination system (sometimes referred to as X0 sex-determination system) is a system that some species of insects, arachnids, and mammals use to determine the sex of offspring. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome (XO), while females have two (XX).
Sexual dimorphism is the condition where sexes of the same species exhibit different morphological characteristics, including characteristics not directly involved in reproduction. [1] The condition occurs in most dioecious species, which consist of most animals and some plants.
Some chromosomal sex determination systems in animals A sex-determination system is a biological system that determines the development of sexual characteristics in an organism . [ 1 ] Most organisms that create their offspring using sexual reproduction have two common sexes, males and females , and in other species, there are hermaphrodites ...
The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors, including Komodo dragons.
A few types of organisms, such as many fungi and the ciliate Paramecium aurelia, [11] have more than two "sexes", called mating types. 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 ...
Elephants can use their ears as threat displays in male-to-male competition. Sexual selection in mammals is a process the study of which started with Charles Darwin's observations concerning sexual selection, including sexual selection in humans, and in other mammals, [1] consisting of male–male competition and mate choice that mold the development of future phenotypes in a population for a ...
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. [1] [2] Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.
In both plants and animals, gamete size difference is the fundamental difference between females and males. [2] Anisogamy most likely evolved from isogamy. [3] Since the biological definition of male and female is based on gamete size, the evolution of anisogamy is viewed as the evolutionary origin of male and female sexes.