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The Human Genome Chapter 14 Human Chromosomes • Karyotype: a picture of the chromosomes from a single cell. • Used to determine the sex, or possible genetic disorders of an individual. • 44 autosomes • 2 sex chromosomes Determining the sex of a zygote: • Always determined by the father. • All eggs contain one X chromosome • Sperm either contain one X chromosome or one Y chromosome. Pedigrees • Used to show how a particular trait is passed from one generation to the next in a family Blood types • Controlled by more than one gene • A, B, O, AB • Rh factor Genetic disorders • Recessive disorders most common • To be afflicted with a recessive disorder, one must have 2 copies of each recessive allele. PKU (phenylketonuria) • The body cannot break down the amino acid phenylalanine • Nutrasweet could be deadly • If not detected early, or if a specific diet is not followed, serious brain damage can occur. • 1 in 60 Caucasians are carriers of the gene that causes PKU. • The gene is found on chromosome 12 Tay-Sachs • Cannot break down certain fats. • Results in brain damage • The gene is found on chromosome 15 • Mainly affects people of European Jewish ancestry (1 in 30 are carriers) Cystic Fibrosis • Affects digestive system and absorption of fats. • Causes a build up of mucus in the lungs. • CF kids are often more likely to develop pneumonia. • One of the first disorders to be actively studied for gene therapy. CF (cont.) • Sweat test • Gene found on chromosome 7 • 1 in 25 people are carriers. • Most lethal autosomal recessive disorder in U.S. • No cure Treatment • Respiratory therapy • Enzyme therapy (DNAse) • Lung transplants Albinism • Lack of pigment in skin, hair, and eyes. • Approx. 1 in 17,000 people • Risks: 1. Eye problems 2. Severe sensitivity to sunburn. Autosomal dominant disorders • Expressed when the dominant allele is present in the genotype. Achondroplasia • A form of dwarfism • The torso is of normal size, but arms and legs are very short. • Average adult height of 4 feet. • 1 in 25,000 births. • Gene is found on chromosome 4 • “Little People” Huntingtons • Results in a loss of muscle control and mental function. • Breakdown of nerve cells in the brain • Approximately 1 in 10,000 births in Europe and N. America • Gene on chromosome 4 • Symptoms after age 30 • Autosomal Dominant Marfan Syndrome • Mutation in the fibrilin gene that makes proteins found in tendons/ligaments • Results in TALL stature • Heart problems • Abe Lincoln was suspected to have M.S. Sickle cell anemia • Codominant disorder found in African Americans. • Red blood cells are misshapen. • Characterized by extreme pain in legs and arms because the cells get stuck in capillaries. • Can be fatal • The gene can prevent Malaria Sickle-cell cont’d • Approx 1000 babies born each year • 1 in 400 African Americans • Possible cure: bonemarrow transplants • Treatment: – Avoid being overly active – Watch your diet Sex-linked genes and disorders • A situation in which an organism’s sex can affect the chances of inheriting a gene. • First studied by Morgan with fruit flies • Most sex-linked genes are found on the X chromosome Color blindness gene • Recessive gene located on the X chromosome. • Men only have one X chromosome, thus only one copy of the color blind gene. Color Blindness Hemophilia • A disorder in which a person’s blood does not clot properly. • Gene found on X chromosome. • 1 in 10,000 males born are afflicted. Hemophilia: • Main type: hemophilia a. Body cannot manufacture a specific protein needed for proper blood clotting. • Traditional treatment: periodic blood transfusions • “Bleeder’s disease” Duchenne muscular dystrophy • Weakening and loss of muscle tissue. • 1 out of 3000 males born in U.S. • Sex-linked/recessive • Caused by absence of dystrophin, a protein that helps keep muscle cells intact. • Genetic disorder website Chromosomal disorders • loss of or gain of part or a whole chromosome. • Nondisjunction - most common chromosomal mutation. • When a gamete contains either an extra or one less chromosome. • Occurs during meiosis. Down Syndrome • Also known as Trisomy 21 because of the presence of an extra chromosome 21. • Symptoms similar to mental retardation • Approx 1 in 800 babies born in U.S. • Chances of having a baby with Down Syndrome increases with the age of the mother. Sex Chromosome Disorders: • Turner’s syndrome: In females, a person only inherits one X chromosome (45,X) • Klinefelter’s syndrome: In males, an extra X chromosome is present (47,XXY) Hutchinson-Guilford Progeria • One mistake in the DNA sequence of the gene, LMNA causes Progeria. (point mutation) • The LMNA gene normally makes a protein called lamin A, and helps maintain the shape and function of the cell. • The mutation causes the gene to produce an abnormal Lamin A protein called progerin. • In children with Progeria, many cells in the body make progerin protein. • As the children age, progerin builds up in these cells causing progressive disease-Rapid aging DNA analysis • Testing for alleles : makes it possible to determine if a person can pass on a particular disorder to his or her children. • DNA fingerprinting Human Genome Project • Began in 1990. • The goal was to analyze the entire human DNA sequence (6 billion base pairs) • Originally scheduled to be completed in 2005 • In June 2003, the map was completed Gene Therapy • Replacing an absent or faulty gene with a copy of a “good” or working gene. • Still considered a radical therapy. • Has not been tested thoroughly. Assignment: • Page 363-364 –1-10, 12,14,17,19,23,25,26,29