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In species that use the XY sex-determination system, parthenogenetic offspring have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), [28] [29] ZZ (male), or WW (non-viable in most species, [31] but a fertile, [dubious – discuss] viable female in a few, e.g ...
In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. [5] Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
The letter O (sometimes a zero) signifies the lack of a Y chromosome. [1] Maternal gametes always contain an X chromosome, so the sex of the animals' offspring depends on whether a sex chromosome is present in the male gamete. Its sperm normally contains either one X chromosome or no sex chromosomes at all.
Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male. Among all the sexual vertebrates, the only examples of true parthenogenesis, in which all-female populations reproduce without the involvement of males, are found in squamate reptiles (snakes and lizards). [1]
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.
Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants. [6] [7] Sexual reproduction also occurs in some unicellular eukaryotes. [2] [8] Sexual reproduction does not occur in prokaryotes, unicellular organisms without cell nuclei, such as bacteria and archaea.
The sex of a baby is available earlier than ever these days, with some at-home kits able to detect the male chromosome in a pregnant woman's blood as early as seven weeks into pregnancy.
Females normally have two X chromosomes while males typically have an X and a Y chromosome. The X chromosome is more active and encodes more information than the Y chromosome, which has been shown to affect behavior. [14] Genetic researchers theorize that the X chromosome may contain a gene influencing social behaviours. [15] [better source needed]