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Most spiders have a variation of the XO system in which males have two different X chromosomes (X 1 X 2 O), while females have a pair of X 1 chromosomes and a pair of X 2 chromosomes (X 1 X 1 X 2 X 2). [1] Some spiders have more complex systems involving as many as 13 different X chromosomes. [1] Some Drosophila species have XO males. [10]
The SHOX gene in the PAR1 region is the gene most commonly associated with and well understood with regards to disorders in humans, [17] but all pseudoautosomal genes escape X-inactivation and are therefore candidates for having gene dosage effects in sex chromosome aneuploidy conditions (45,X, 47,XXX, 47,XXY, 47,XYY, etc.).
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).
This is an accepted version of this page This is the latest accepted revision, reviewed on 16 February 2025. Cell division producing haploid gametes For the figure of speech, see Meiosis (figure of speech). For the process whereby cell nuclei divide to produce two copies of themselves, see Mitosis. For excessive constriction of the pupils, see Miosis. For the parasitic infestation, see Myiasis ...
Multiple studies in mice have also found largely normal male-type germ cells in XX males soon after birth, but a progressive loss with maturation. [19] [20] Due to its often-subtle presentation, many XX males remain undiagnosed until seeking treatment for infertility in adulthood; it's likely a significant proportion of cases remain undiagnosed.
The development of sexual differences begins with the XY sex-determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote. [3] Females typically have two X chromosomes, and males typically have a Y ...
The introduction of DSBs in DNA often employs the topoisomerase-like protein SPO11. [3] CO recombination may also be initiated by external sources of DNA damage such as X-irradiation, [4] or internal sources. [5] [6] There is evidence that CO recombination facilitates meiotic chromosome segregation. [2]
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.