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In humans and many other species of animals, the father determines the sex of the child. In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.
Some species, such as some snails, practice sex change: adults start out male, then become female. In tropical clownfish, the dominant individual in a group becomes female while the other ones are male, and bluehead wrasses (Thalassoma bifasciatum) are the reverse. Life cycle of clownfish
Instead, sex is determined by the number of X chromosomes. The D. melanogaster Y chromosome does contain genes necessary for male fertility. So XXY D. melanogaster are female, and D. melanogaster with a single X (X0), are male but sterile. There are some species of Drosophila in which X0 males are both viable and fertile. [citation needed]
However, selection for ornamentation within this species suggests that showy female traits can be selected through either female–female competition or male mate choice. [59] Since carotenoid-based ornamentation suggests mate quality, female two-spotted guppies that develop colorful orange bellies during breeding season are considered ...
The chromosome number n = 9 is the basic number in many species of Marchantiales. In some species of Marchantiales, plants with various ploidy levels (having 18 or 27 chromosomes) were reported, but this is rare in nature. [14] 11 Thale cress (Arabidopsis thaliana) 10 12 Swamp wallaby (Wallabia bicolor) 10/11: 11 for male, 10 for female [15] 13
individuals are either male or female. [20] The term "gonochorism" is usually applied to animals while "dioecy" is applied to plants. [21] Gonochorism is the most common sexual system in animals, occurring in 95% of animal species. [22] Gynodioecy: females and hermaphrodites coexist in the same population. [11] Gynomonoecy
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.
Extant primates exhibit a broad range of variation in sexual size dimorphism (SSD), or sexual divergence in body size. [4] It ranges from species such as gibbons and strepsirrhines (including Madagascar's lemurs) in which males and females have almost the same body sizes to species such as chimpanzees and bonobos in which males' body sizes are larger than females' body sizes.