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 mother’s 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