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Human Genetics Human Genetic Disorders • Genetic abnormality = a genetic condition that is a deviation from the average: not life-threatening • Genetic disorder = describes conditions that cause medical problems Karyotype • A pictorial display of metaphase chromosomes from a mitotic cell • Chromosomes are identified and arranged by their characteristic size, shape, centromere location and staining patterns Human Karyotype Amniocentesis Detects some fetal abnormalities through karyotyping Human Chromosome Characteristics • Diploid set for humans = 46 • Autosomes = 22 • Female-sex chromosomes = homologous (XX) • Male-sex chromosomes = non-homologous (XY) Autosomal Recessive • Either parent can carry the recessive allele on an autosome. – Heterozygotes are symptomfree. – Homozygotes are affected. Genetic Errors of Metabolism • One defective or absent gene can result in the inability to make a specific enzyme • Recombinant DNA techniques may someday correct faulty chromosomes Obesity gene discovered Genetic Errors of Metabolism • Galactosemia –Inability to metabolize lactose • Cystic Fibrosis –Inability to breakdown mucous in lungs and other organs Tay-Sachs Disease • Missing an enzyme to break down lipids, leading to destruction of central nervous sys. • Mainly found in Eastern European Jewish decendents 1:27 is a carrier – Judaism is trying to eliminate gene through non-breeding between couples who are carriers Sickle-cell Anemia • Recessive, changes the shape of the hemoglobin molecule – Extremely painful, debilitating – Only distorts when deoxygenated Sickle-cell Anemia • High frequency in black populations • SS= no sickle-cell • Ss = mild symptom • ss = full blown disease Heterozygote Superiority • Heterozygotes receive protection from symptoms of sickle-cell AND malaria advantage in malarial countries • SS + malaria = malaria only • Ss + malaria = no symptoms of either • ss + malaria = mild sickle cell Complications • Sickle cells become trapped and destroyed in the spleen causing Splenic Sequestion • Anemia • Pain episodes • Stroke or Brain Damage • Kidney failure • Pneumonia • Increased Infections PKU • Lack one enzyme to break down phenylalanine – Products accumulate, cause mental retardation, other severe symptoms – Treated through dietary restrictions Autosomal Dominant • A dominant allele is always expressed and if it reduces the chance of surviving or reproducing, its frequency should decrease • Mutations and conditions that set in late in life work against this Autosomal Dominant • Achondroplasia (Dwarfism) –Lacks functional gene for somatropic hormone in the pituitary Errors in Metabolism • Acromegaly (Gigantism) – Pituitary produces excess growth hormones Huntington’s Disorder • A serious degeneration of the nervous system with an onset from age 40 onward - Fatal, no cure Would you want to know? • Gene has been found WHY??? Woody Guthrie X-Linked Recessive • Mutated gene occurs only on the X chromosome X-Linked Recessive • Heterozygous females are phenotypically normal • Males are affected because they have only one allele for the trait (on the X chromosome) and it can be recessive. X-Linked Recessive • Color-blindness • Baldness Hemophilia A • Inability of blood to clot because genes do not code for clotting agent(s) Queen Victoria: a Carrier Hemophilia A • Afflicted persons need frequent transfusions and infusions of artificial clotting agents • Internal bleeding from falls or bruising the most serious • Cummulative scarring may restrict movement X-Linked Dominance • Similar to X-linked recessive alleles, except the allele is also expressed in heterozygous females • Examples: faulty enamel (of the teeth) trait Patterns of Inheritance • Aneuploidy = one extra or one less chromosome, may affect one of every two newly fertilized eggs • Polyploidy = three or more of each chromosome, is common in plants but is lethal to the zygote if it occurs in humans Meiotic Errors • Nondisjunction- homologues don't separate in meiosis 1 Nondisjunction in Sex Chromosomes • Homologues don't separate in meiosis 1 Trisomy 21/Down Syndrome • Occurs more frequently in children born to older women and men – 1 in 80 births after 40 yrs – 1in 40 births after 45 yrs Down Syndrome • Most children show mental deficiencies – Many lead productive lives – 40% have heart defects – many have diabetes and have weight issues Turner Syndrome • XO – Females with only one X chromosome, mostly due to nondisjunction in father – Most are spontaneously aborted – Sterile, short stature, heart defects, premature aging, shorter lives • YO = LETHAL Klinefelter Syndrome • XXY condition – Most from non-disjunction in mother – Tall, some mental slowness – Poor male sex organ development; breast development; usually sterile Jacob Syndrome • XYY condition • Fertile, tall, slight retardation, increased strength & aggression • NOT predisposed to crime - a fallacy Changes in Chromosome Structure • Translocation – Transfer of a piece of one chromosome to another Changes in Chromosome Structure • Deletions – Loss of a chromosome region by viral attack, chemicals, irradiation, or other environmental factors Cri-du-Chat • Deletion or translocation of material from 5th chromosome –“Cry of the Cat” (French) - sound many children make when crying – Severe mental retardation; internal problems Changes in Chromosome Structure • Inversion – Alters the position and sequence of the genes so that gene order is reversed Changes in Chromosome Structure • Duplications – Occurs when a gene sequence is in excess of the normal amount. Duplications • Fragile X syndrome – Mental retardation – Repeats that may block expression of gene on X chromosome Mistake Summary Designed by Anne F. Maben These images are for viewing only and may not be published in any form