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Other species (including most Drosophila species) use the presence of two X chromosomes to determine femaleness: one X chromosome gives putative maleness, but the presence of Y chromosome genes is required for normal male development. In the fruit fly individuals with XY are male and individuals with XX are female; however, individuals with XXY ...
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]
Females with more than one extra copy of the X chromosome (48, tetrasomy X or 49, pentasomy X) have been identified, but these conditions are rare. Turner syndrome: This results when each of a female's cells has one normal X chromosome and the other sex chromosome is missing or altered.
In humans, X-chromosome inactivation enables males and females to have an equal expression of the genes on the X-chromosome since females have two X-chromosomes while males have a single X and a Y chromosome. X-chromosome inactivation is random in the somatic cells of the body as either the maternal or paternal X-chromosome can become ...
[28] [29] One of the female's X chromosomes is randomly inactivated in each cell of placental mammals while the paternally derived X is inactivated in marsupials. In birds and some reptiles, by contrast, it is the female which is heterozygous and carries a Z and a W chromosome while the male carries two Z chromosomes.
Klinefelter’s syndrome occurs when a man is born with one or more extra X chromosomes, leading to a variety of impacts that include underdeveloped testicles, impaired testosterone production ...
One of the X chromosomes is homologous to the human X chromosome, and another is homologous to the bird Z chromosome. [18] Although it is an XY system, the platypus' sex chromosomes share no homologues with eutherian sex chromosomes. [19]
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).