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Mutations When something goes wrong… Causes of Mutations • Mutations are caused by changes in the nucleotide sequence of DNA (A, T, C, G) or of a gene (specific area of a chromosome) • This can occur: – During DNA replication – During cell division – After cell division Mutations Types • Germ-Cell Mutations – Occur in an organism’s sex cells – Do not affect the organism itself but may be passed to offspring • Somatic-Cell Mutations – Take place in an organisms body cells and can affect the organism – Cannot be inherited • Lethal Mutations – Cause death, often before birth Gene Mutations Gene Mutations • Point mutations affect a single nucleotide • Base pair substitutions switches a nucleotide – Silent mutation • Does not change the amino acid – Missence mutation • Change of a single amino acid – Nonsense mutation • Changes amino acid to stop codon – Neutral mutation • Changes amino acid to chemical similar amino acid Gene Mutations • Frameshift Mutation – Change in reading frame due to adding or deleting a nucleotide AAT TGC CCG ACT TTT CGC CAT • Add A after 2nd nucleotide AAA TTG CCC GAC TTT TCG CCA T Chromosomal Mutations Chromosomal Mutations • These mutations can be detected by karyotyping – Nondisjunction • Homologous chromosomes or chromatids don’t split in division – Deletion • Loss of a piece of chromosome due to breakage – Duplication • Portion of the chromosome can be duplicated – Inversion • Part breaks off, then reattaches in reverse position – Translocation • Part breaks off, reattaches to a non-homologous chromosomes – Insertion • Extra DNA is inserted into a non-homologous chromosome Effects of Mutations • Always result in changes to genotype (DNA) but not always phenotype (what you see!) – Neutral • No effect – Beneficial • Enhances fitness – Deleterious • Decreases fitness Cystic Fibrosis Cystic Fibrosis • Genetic disorder affecting the respiratory and digestive system caused by defective gene on Chromosome 7 – 1000 different mutations in this gene have been identified – Most often caused by deletion of a single amino acid • Body produces a mucous that clogs the airways and increases risks of infection • Both parents must pass on the gene to their children – More than 10 million Americans carry the gene and don’t know it • About 2,500 babies are born with cystic fibrosis in the U.S. each year. Turner Syndrome Turner Syndrome • Caused by missing or incomplete X chromosome often due to non-disjunction • Women with Turner syndrome are usually sterile and cannot have children • Short in stature, stocky appearance, arms that turn out slightly at the elbow, receding jaw line, short webbed neck, and low hairline • Affects 60,000 females in the United States. This disorder is seen in 1 of every 2000 to 2500 babies born, with about 800 new cases diagnosed each year • In 75-80% of cases, the single X chromosome comes from the mother's egg; the father's sperm that fertilizes the egg is missing its sex chromosome Klinefelter Syndrome Klinefelter Syndrome • Caused by an extra X chromosome (XXY) in males due to by nondisjuction • Males are often tall and don’t develop secondary sex characteristics (facial hair, underarm hair, etc) • Often not diagnosed until puberty (less muscular body, more breast tissue, less hair) or when men try to have children due to sterility • Treated with hormone replacement therapy – testosterone injections • Klinefelter syndrome is one of the most common genetic abnormalities. It affects between 1 in 500 and 1 in 1,000 males. Sickle Cell Disease Sickle Cell Disease • Mutation on a gene on chromosome 11 that codes for the shape • Blood cells get stuck in the blood vessels and cannot transport oxygen, resulting in pain and damage to organs, leading to low red blood cell counts • Both parents must pas a defective gene to their children • Daily penicillin to prevent infections, folic acid to build new cells, blood transfusions, bone marrow transplant • Unlike normal red blood cells, which can live for 120 days, sickle-shaped cells live only 10 to 20 days. • In the United States, the disease most commonly affects African-Americans. About 1 out of every 500 AfricanAmerican babies born in the United States has sickle cell anemia