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Genetic Disorders Overview • 6 billion base pairs of DNA ~ 3 meters of DNA • Approximately 30,000 – 70,000 genes * Approximately 80-100,000 proteins • These genes are spread across 24 different chromosomes **One chromosome each from each parent, for a total of 23 pairs, or 46 chromosomes per cell** • All normal human cells (except sex cells) have 46 chromosomes, half of which are from mom, and the other half are from dad. (23 pairs of homologous chromosomes) • 2 sets (46) of homologous chromosomes =DIPLOID • Pictures of chromosomes grouped in order and in pairs = Karyotype Karyotype Normal male Chromosome Number Homologous chromosomes Diploid! Dark bands = Genes Autosomal chromosomes Sex = non sex determining chromosomes, chromosomes same shaped homologous Sex chromosomes: X/Y = male X = female, Y = male X/X = female …still sex determination Dad • Probability of having a boy or a girl. Mom X Y X XX XY X XX XY X Y 50% chance for boy 50% chance for girl X X Girl Boy Girl Boy Chromosomal disorders • What if you have extra chromosome? • What if you are missing a chromosome? Chromosomal disorders usually: Increase chance of having disorders, such as mental retardation, sterility, and decrease life expectancy. Is anything wrong? Male Chromosome 21 trisomy Down syndrome Trisomy 21( extra on the 21st)- Down Syndrome • Redundant neck fold/flat occipital (back of the head) • Low set ears • Protruding/large tongue * Wide space between 1st & 2nd toes Trisomy 13 (47,XY,+13) – Cleft Lip Cleft Lip- a split or indentation in the lip of a newborn baby. Sex Chromosome Abnormalities • • • • Turner syndrome Klinefelter syndrome (XXY) Triple X XYY Is anything wrong? X Turner’s syndrome Turner Syndrome • 45 Chromosomes , only one sex chromosome • The incidence is about 1 in 5000 female births but this is only the tip of the iceberg because 99% of Turner syndrome embryos are spontaneously aborted. • Individuals are very short, they are usually infertile. • Characteristic body shape changes include a broad chest with widely spaced nipples and may include a webbed neck. • IQ and lifespan are unaffected. Is anything wrong? XXY Klinefelter’s syndrome • Klinefelter Syndrome 47,XXY *The incidence at birth is about 1 in 1000 males. *Testes are small and fail to produce normal levels of testosterone which leads to breast growth in about 40% of cases and to poorly developed secondary sexual characteristics. *Males are sterile. *These males are taller and thinner than average and generally have a slight reduction in IQ (10-15 points below sibs). Many Kleinfelter males lead a normal life. *Very rarely more extreme forms of Kleinfelter's syndrome occur where the patient has 48, XXXY or even 49, XXXXY karyotype. These individuals are generally severely handicap. XXX Syndrome XXX Syndrome Triple X syndrome is not inherited, but usually occurs as a random event during the formation of the reproductive cells. *There may be a growth spurt until the age of approximately eight years of age, resulting in a taller than average final height *They often have a increased risk of learning disabilities and delayed speech and language skills. *They have a slightly lower intelligence level than their siblings (the IQ may be ten to fifteen points lower than their siblings). *Females with this condition are not at any increased risk for medical problems. XYY Syndrome Men who have XYY's syndrome are substantially taller, tend to be wiry-built, and tend to have severe acne. Minor birth defects -- like pectus, crooked eye, and minor outturning of the elbows, are supposed to be common in XYY's. Color Blindness Colorblindness • 3 human genes associated with color vision are located on the X chromosome. • Because males have one X chromosome, all the genes will be expressed, even if they are recessive.