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The XY sex-determination system is a sex-determination system present in many mammals, including humans, some insects , some snakes, some fish , and some plants (Ginkgo tree). In this system, the sex of an individual usually is determined by a pair of sex chromosomes .
The XX/XY sex-determination system is the most familiar, as it is found in humans. The XX/XY system is found in most other mammals, as well as some insects. In this system, females have two of the same kind of sex chromosome (XX), while males have two distinct sex chromosomes (XY).
The female-biased sexual size dimorphism observed in many taxa evolved despite intense male-male competition for mates. [28] In Osmia rufa, for example, the female is larger/broader than males, with males being 8–10 mm in size and females being 10–12 mm in size. [29] In the hackberry emperor females are similarly larger than males. [30]
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.
Chromosomal sex is determined at the time of fertilization; a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell. Gonadal sex refers to the gonads, that is the testicles or ovaries, depending on which genes are expressed. Phenotypic sex refers to the structures of the external and internal genitalia. [6]
In a large number of organisms, the sex-determination systems presently observed are products of sex chromosome turnover. Sex chromosome turnover is a process defined as when the type of the sex chromosome changes as a product of a change in the identity of the sex-determining genes (such as by mutation) or by a change in their location. [ 28 ]
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Pages in category "Sex-determination systems" The following 26 pages are in this category, out of 26 total. This list may not reflect recent changes. ...