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Diseases and karyotypes • Definitions • Autosomes- any chromosome that is not a sex chromosome. Not the “X” or “Y” • Sex-linked- genes located on the sex chromosome. Usually on the “X” • Nondisjunction- A chromosome mishap in meiosis Abnormal numbers of autosomes • Metaphase chromosomes are photographed; • the chromosome pictures are then enlarged and • arranged in pairs by a computer according to length and location of the centromere. Abnormal numbers of autosomes • This chart of chromosome pairs is called a karyotype, and it is valuable in identifying unusual chromosome numbers in cells. • A Karyotype is a photograph of the chromosomes of a single cell. Another view Normal Female Normal Male ? Colchicine added to cells Cells broken open Picture of chromosomes taken Microscope zooms in Chromosomes cut up and arranged Chromosomal Disorders Individuals are missing a chromosome or have an extra chromosome Down syndrome: Trisomy 21 • Down syndrome is the only autosomal trisomy in which affected individuals survive to adulthood. • It occurs in about one in 700 live births. Down syndrome: Trisomy 21 • Down syndrome is a group of symptoms that results from trisomy of chromosome 21. • Individuals who have Down syndrome have at least some degree of mental retardation. • The incidence of Down syndrome births is higher in older mothers, especially those over 40. Chromosome 21 Abnormal numbers of sex chromosomes • Many abnormalities in the number of sex chromosomes are known to exist. • An X chromosome may be missing (designated as XO) or there may be an extra one (XXX or XXY). There may also be an extra Y chromosome (XYY). Klinefelter’s Syndrome XXY • Poor beard growth • Tend to grow fewer chest hairs • Breast development • Wide hips • Long legs • Narrow shoulders Karyotype of a male with Klinefelter’s syndrome •Short (<59”) XO •Webbed neck •Sterile •Low hairline Karyotype of a female with Turner’s syndrome Autosomal Genetic Disorders • These are a result of genes on the 22 pairs of chromosomes that are not the sex chromosomes (not X and Y) Sickle Cell Anemia • Autosomal Recessive • Affects the blood • Symptoms: impaired blood circulation, organ damage • Defect: Abnormal hemoglobin molecules – RBC’s • 1/500 African Americans -If heterozygous will not get malaria Sickle-cell disease • Abnormally shaped blood cells, slow blood flow, block small vessels, and result in tissue damage and pain. Normal red blood cell Sickle cell Cystic Fibrosis • Recessive allele • Affects the lungs and digestive tract • Characterized by thick mucus in lungs and digestive tract • Food is not digested properly • Breathing is difficult - frequent lung infections • .Most common lethal genetic disorder in white Americans. • Approximately one in 28 white Americans carries the recessive allele, and one in 2500 children born to white Americans inherits the disorder. Cystic Fibrosis On chromosome 7 there is a mutation in a gene that causes a thick mucus to develop This is a frame shift mutation • Autosomal dominant—carriers GET the disease • Affects the central nervous system • Causes nerve death in the brain. Starts with spasms and eventually leads to a vegetable like state and death. Onset between 30 and 50. Huntington’s Disease Huntington disease affects an estimated 3 to 7 per 100,000 people of European ancestry. The disorder appears to be less common in some other populations, including people of Japanese, Chinese, and African descent. Defect on Chromosomes number 4 Typical Pedigree of Huntington’s Disease I 1 2 II 2 1 4 3 5 III 1 2 3 4 5 Phenylketonuria (PKU) • Autosomal recessive • Affects: brain • Symptoms: Failure of brain to develop in infancy; if untreated causes death. • Defect: Caused by absence of enzyme that converts phenylalanine to tyrosine (amino acids) • 1/18,000 urine test, treated by diet until puberty. Phenylketonuria (PKU) • Most common in people of Norwegian and Swedish descent. Symptoms of PKU • New born appears normal. • Once baby starts drinking milk, which is high in phenylalanine, damage occurs Symptoms • Build up in phenylalanine causes severe central nervous system damage resulting in mental retardation. Treatment of PKU • All newborns are tested for PKU. • Changes in diet can prevent damage. Given a diet low in phenylalanine until the brain is fully developed. Phenylketonuria Phenylketonurics: Contains Phenylalanine Tay-Sachs disease • Tay-Sachs (tay saks) disease is a recessive disorder of the central nervous system. • In this disorder, a recessive allele results in the absence of an enzyme that normally breaks down a lipid produced and stored in tissues of the central nervous system. • Because this lipid fails to break down properly, it accumulates in the cells. Symptoms of Tay-Sachs Disease • Blindness • Progressive loss of movement • Mental deterioration • Death by age 5. I 1 2 Typical Pedigree for Tay-Sachs II 1 2 3 4 1 2 III 3 IV 1 Sex-linked traits • These are genes that are found on the X chromosome. They are generally more common in males than in females. • Females need to have it on both their X chromosomes ( get from mom and dad) • Since males only have 1 X chromosome, they only need to have received the allele from their mother for the trait to show. Sex-linked trait Hemophilia • X-linked recessive • Defect: defective form of blood-clotting agent. • Symptoms: failure of blood to clot • About one male in every 10 000 has hemophilia, but only about one in 100 million females inherits the same disorder. Hemophilia: An X-linked disorder • Males inherit the allele for hemophilia on the X chromosome from their carrier mothers. One recessive allele for hemophilia will cause the disorder in males. • Females would need two recessive alleles to inherit hemophilia. • Some genetic disorders are both genetic and environmental. People inherit the tendency to a trait, but how and when it is expressed depends on environmental factors such as diet, exercise, exposure to chemicals, etc. Diabetes Asthma Cardiovascular Disease