Abnormal Sex Chromosomes

• Standard karyotype designations indicate both the total number of chromosomes and the sex chromosomes present
• nondisjunction: chromosomes do not separate in meiosis
• Nondisjunction of the X chromosome in oogenesis can lead to eggs with 2 X's or no X's
• Fertilization of an O egg with an X sperm gives XXX; with a Y sperm gives XXY
• Fertilization of an O egg with an X sperm gives XO but YO is not a viable embryo
• Nondisjunction of the XY pair in Meiosis 1 of males can lead to XY sperm and O sperm
• Nondisjunction in Meiosis 2 of males can lead to XX sperm, YY sperm, and O sperm
• If an XX sperm fertilizes a normal X egg, XXX individuals can occur
• If an O sperm fertilizes an X egg, XYY individuals result
• 47:XXX is Triplo X and leads to a fertile female. This occurs every 1 in 1000 females
• 47:XXY is Kinefelters and leads to a sterile male. This occurs every 1 in 500 males
• 47:XYY is XYY or Jacobs and leads to a fertile male. It occurs every 1 in 1000 males
• 45:XO is Turner's and leads to a sterile female. It occurs every 1 in 3000 females
• 45:YO is lethal
• Triplo X females are typically taller and have somewhat lower IQ than normal. They are fertile but are more likely to become infertile as they get older
• Kilnefelters males are taller than normal and have small testes. At puberty, they often show breast development and often have to receive shots of testosterone
• Jacob's syndrome are taller than normal and have a somewhat reduced IQ
• Turner's syndrome females are very short and have very flat chests and non functional ovaries
• XYY can occur with nondisjunction
• XYY males may be slightly larger than average and have an increased risk of criminal behavior
• Early in embryology, all fetuses develop ovotestes
• Around 7 weeks after fertilization, a gene on the Y called sry that encodes TDF becomes active. TDF is a transcription factor that causes the ovotestes to become testes
• If there is no sry gene function, the ovotestes develop into ovaries that produce estrogen
• At puberty, the hypothalamic hormones induce pituitary to make and release gonadotropic hormones such as FSH and LH that in females causes an ovarian follicle to develop and release estrogen and progesterone which turns off FSH and LH production
• Most genes involved in making sex hormones are not on the X or Y chromosomes
• A defective sry gene gives Swyer syndrome, female phenotype but sterile and lacks estrogen
• Tfm or Complete Androgen Insensitivity syndrome is caused by a lack of testosterone receptors. The individual develops as a phenotypic female with a blind vagina and undescended testes. This gene is on the X chromosome
• Guevedoces results when a gene for an aromatase needed to complete male development isnt activated until puberty. At that time, the ambiguous genitalia complete development into male structures
• Males usually have higher SAT math scores
• Girls score higher in verbal fluency
• Normal human female karyotype: 46; XX
• The use of testosterone is not beneficial to XY individuals with the tfm gene because they have no testosterone receptors