Chromosomes Cytogenetics: study which links chromosome variations to specific traits Chromosome: Dark heterochromatin (repetitive DNA) Light euchromatin (protein- encoding genes) Telomeres: tips (repeats of TTAGGG) Centromere: constriction that attaches to spindle Repeats of a 171 base DNA sequence (alpha satellite) Replicated during the end of S phase Karyotype: a chromosome chart (22 pairs of autosomes/1 pair of sex chromosomes) Chromosome Studies: Amniocentesis: removal of small sample of fetal cells and fluid from the uterus Between weeks gestation (Usually pregnant women over 35) Can detect at least 800 of 5,000 biochemical problems Most common abnormality detected trisomy Chorionic Villus Sampling: cells from chorionic villi (develop into placenta Earlier results (10-12 weeks) Less accurate than amniocentesis Disadvantage: spontaneous abortion Fetal Cell Sorting: separates fetal cells from the mothers bloodstream uses fluorescence-activated sorter Safer, newer, experimental Ideogram: graphical representation of a specific chromosome Bands appear as stripes FISH highlights (paints) individual genes (Fluorescence In situ Hybridization) Abnormal chromosome numbers account for at least 50% of spontaneous abortion Polyploidy: extra sets of chromosomes 17% of spontaneous abortions Common among flowering plants; Colchicine (alkaloid from autumn crocus) interferes with spindle formation Seedless watermelon, Winesap apples Aneuploidy: + or a single chromosome (due to nondisjunction) Many spontaneous abortions; mental retardation Monosomy: 1 less than the normal diploid number (2N-1 = 45) Turner Syndrome: (45; X_) Short, sterile female; 1 in 2,000 female births; Sexually underdeveloped; normal intelligence; skin flaps on back of neck; broad shield-like chest Trisomy: 1 more than the normal diploid number (2N+1 = 47) Down Syndrome: 1 infant in every 800 live births; Extra #21; Epicanthic folds in eyelids; flat face, poor muscle tone; short fingers; short stature; suppressed immunity; developmental problems; mentally challenged; life span of 50 years; ovum as the source of the problem in 90% of the cases; older adults with Alzheimer Disease; decreased risk of cancer (extra copy of DSCRI gene suppresses angiogenesis Klinefelter Syndrome: (XXY) Sterile male underdeveloped sexually (prostate, testes); breast development (gynecomastia); 1 in 660 male births; long limbs with large hands and feet; decreased intelligence Jacobs Syndrome (XYY) Increased height; acne; speech and reading problems Triplo-X (XXX) Taller female with menstrual irregularities; 1 in 1,000 female births; sterile; delayed language development and motor skills Abnormal Chromosome Structures Deletion: missing genes Cri-du-chat Syndrome: deletion of part of #5; high pitched cry; mentally challenged; pinched features; gastrointestinal and cardiac complications; abnormal development of larynx and glottis Duplication: region of chromosomes where genes are repeated Translocation: pieces break off and connect to a different chromosome spontaneous abortions and birth defects Inversion: part of chromosome has flipped around Fragile Sites in Human Chromosomes Susceptible to chromosome breakage Fragile X Syndrome (Mortin-Bell Syndrome) Most common mentally challenged inherited condition Long narrow face with protruding chin, enlarged ears Increased testicular size (gynecomastia) Gene = FMR1 (sequence of 3 nucleotides repeated many times) Link between an autosomal fragile site and lung cancer Specialized Chromosomes Polytene Chromosomes: salivary, rectal, midgut Can be seen in interphase Individual bands called chromomeres Undergo uncoiling (puff) in Drosophila Lampbrush Chromosomes: meiotic chromosomes In vertebrate oocytes and insect spermatocytes