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Turner syndrome (TS), commonly known as 45,X, or 45,XO, [note 1] is a chromosomal disorder in which cells have only one X chromosome or are partially missing an X chromosome (sex chromosome monosomy) leading to the complete or partial deletion of the pseudoautosomal regions (PAR1, PAR2) in the affected X chromosome.
The relevant nondisjunction in meiosis I occurs when homologous chromosomes, in this case the X and Y or two X sex chromosomes, fail to separate, producing a sperm with an X and a Y chromosome or an egg with two X chromosomes. Fertilizing a normal (X) egg with this sperm produces an XXY or Klinefelter offspring.
Turner syndrome, also known as 45,X or 45,X0, is a chromosomal abnormality characterised by a partial or completely missing second X chromosome, [4] [24] [25] giving a chromosomal count of 45, instead of the typical count of 46 chromosomes.
46,XX/46,XY is an example of tetragametic chimerism because it requires four gametes – two sperm and two ova. 46,XX/46,XY is most commonly explained during in conception combination of two fertilized eggs zygotes. Two ova from the mother are fertilized by two sperm from the father. One sperm contains an X chromosome; the other contains a Y ...
Human conditions due to monosomy: Turner syndrome – Females with Turner syndrome typically have one X chromosome instead of the usual two X chromosomes. Turner syndrome is the only full monosomy that is seen in humans — all other cases of full monosomy are lethal and the individual will not survive development.
In a normal situation, all the cells in an individual will have 46 chromosomes, with one being an X and one a Y or with two Xs. However, sometimes during the early copying processes of DNA replication and cell division, one chromosome can be lost. In 45,X/46,XY, most or all of the Y chromosome is lost in one of the newly created cells.
Turner syndrome occurs due to partial or complete absence of one of the X chromosomes, resulting in 45,XO or 45,X. Some associated characteristics include short stature, a broad shield-like chest, webbed neck, premature ovarian failure, and heart and kidney abnormalities. [ 8 ]
The purple cell has 2 Y-chromosomes and 1 X-chromosome caused by the ovum fusing with a sperm cell with two Y-chromosomes, which was due to division problems in MII of the male. 47,XYY is not inherited; it usually occurs as a random event during the formation of sperm cells.