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Transcript
5/15/2016 Causes of Genetic Disorders • Genetic disorder – abnormal condition that a person inherits through genes or chromosomes. Human Genetic Mutations What is a mutation? • A mutation is a permanent alteration in a sequence of DNA that makes up a gene. • Types of Gene Mutations: –Deletion –Inversion –Translocation –Insertion –Duplication –Substitution • Some are caused by mutations in the DNA of genes. (Gene Mutations) • Others are caused by changes in the overall structure or number of chromosomes. (Chromosomal Mutations) Gene Mutations • Small scale: one gene is affected. • Large Scale: multiple genes are affected. • Any change to the DNA sequence of a gene: -Nucleotides/Bases may be added, missing, or changed Gene Deletion Cystic Fibrosis & Cri du Chat • Body produces abnormally thick mucus in the lungs and intestines making it hard to breathe. • Infants often have a high-pitched cry that sounds like that of a cat. Results intellectual disability and delayed development. Changes the number of DNA bases by removing one or more genes (pieces of DNA). One or more genes are removed Causes: Wolf-Hirschhorn syndrome, Cri du Chat syndrome, Cystic Fibrosis 1 5/15/2016 Gene Inversion Cleft Palate and Club Foot • Cleft Palate affects the top of the mouth – a gap/opening exists. • Club Foot is where the foot is twisted out of shape or position. An entire section of DNA is reversed or flipped end-to-end on a a segment of genes flip end-to-end on the chromosome chromosome. Causes: cleft palate, club feet Gene Translocation Gene Insertion Increases the number of DNA bases in a gene by adding a piece of DNA. AMaterial whole chromosome or chromosome segment is swapped with another chromosome attaches to another chromosome or segment creating a hybrid. Causes: Causes: Burkitt’s Lymphoma Huntington’s Disease and Fragile X Syndrome (cancer of the lymph nodes, in children) Huntington’s Disease & Fragile X • Huntington’s Disease causes nerve cells in the brain break down over time. Gene Duplication • Fragile X syndrome causes a range of developmental problems including learning disabilities and cognitive impairment. A segment genes twice and added to A piece of DNA isofcopied oneisorcopied more times. the chromosome Causes: Charcot–Marie–Tooth disease (high arched foot, claw feet, confined to a wheelchair) 2 5/15/2016 Gene Substitution Charcot–Marie–Tooth disease • Charcot-Marie-Tooth disease is characterized by loss of muscle tissue and touch sensation, predominantly in the feet and legs but also in the hands and arms in the advanced stages of disease. A piece of DNA exchanges one base for another. (add this to the bottom of your page) Causes: Sickle Cell Anemia Sickle- Cell Disease • The Hemoglobin shape in blood changes, causing blood cells to have a sickle shape. • The sickle shape can clog blood vessels and cannot carry as much O2 as normal shaped red blood cells. • A person must have 2 alleles for this gene to have this disease. Chromosomal Mutations • Any change in the structure or number of chromosomes • A chromosome mutation causes individuals to have an abnormal number of chromosomes. What are chromosomes? • Humans have 23 pairs of chromosomes, with one chromosome from each parent. • The chromosomes are coiled up DNA. • Under normal conditions all of the chromosomes are inherited in tact. Down Syndrome • Cause: Nondisjunction of chromosome 21 • Three copies of chromosome 21 = “TRISOMY 21” 3 5/15/2016 Warkany Syndrome Edward Syndrome • Cause: An additional copy of chromosome 18 in some or all of the cells in the body. • Three copies of chromosome 18 = “TRISOMY 18” Patau Syndrome • Cause: An extra 13th chromosome. • Three copies of chromosome 13 = “TRISOMY 13” • Can cuase severe intellectual disability and physical defects. • Also known as cleft lip Klinefleter Syndrome • Cause: An extra copy of chromosome 8. • Three copies of chromosome 8 = “TRISOMY 8” • Characteristics: • Uneven legs • Curved bones • Creases in feet and hands Turner Syndrome • Cause: A complete or partial absence of the second sex chromosome. – XO instead of XX • A chromosomal disorder that affects only females. • Tend to be smaller in size and have some exaggerated features. Genetic Screening - Amniocentesis • Cause: A genetic condition in which a boy is born with an extra copy of the X chromosome. – XXY instead of XY • Tend to have more feminine like characteristics. 4