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Mutations Mutations are defined as “a sudden genetic change in the DNA sequence that affects genetic information”. They can occur at the molecular level (genes) and change a single gene, or at the chromosome level and affect many genes. Things that can cause mutations are called “mutagens”. Known mutagens are ultraviolet light, cigarette smoking, certain chemicals like PCB’s. Effects of Mutations Silent mutations - have no effect on the expression of the gene. Causes for this type of mutation: It is in a non-coding region It does not change the amino acid sequence The change does not affect the folding of the protein Inheritability of Mutations It depends on where it occurs i. Germ mutations – occur in gametes. Inheritable (colorblindness, hemophilia) ii. Somatic mutations – affect body cell, not inheritable (cancer) Types of Mutations – mistakes a) Gene (point) Mutations – effects a single gene i. Substitution ii. Frameshift a) Chromosomal mutations – most drastic, change in structure or # of chromosomes (affects many genes) III. Point Mutations a) Substitution – one base exchanges for another, affects 1 amino acid (Ex. GCA-TCA GCT-TCA Effects of substitution mutations Missense mutations – causes a change in the amino acid coded for Nonsense mutations – causes a stop codon to occur prematurely a) Frameshift – affects several amino acids -Insertion – 1 base is inserted, affects several amino acids Ex. (GCA-TCA GCA-GTC-A -Deletion – base is removed, affects several amino acids Ex. (GCA-TCA GCT-CA Chromosome mutations Nondisjunction – incomplete chromosome division during meiosis; results in gametes with too many or too few chromosomes. Ex: Down syndrome is caused by an extra #21 chromosome Polyploidy Aneuploidy Down’s Syndrome •Trisomy 21 •1 in 700 births •Mental retardation •Males are sterile but females are not Likelihood of chromosomal mutations 1 in 1700 for mothers < 20. 1 in 1400 for mothers >20<30. 1 in 750 for mothers >30<35. 1 in 16 for mothers >45. Sex chromosome disorders – occurs as a result of nondisjunction of the sex chromosomes Ex: Turner’s syndrome – X-; Klinefelter’s syndrome – XXY. Klinefelter’s Syndrome •XXY •1 in 1,000 •Usually sterile because of low sperm count •Tall, sparse body hair •Suffer from gynecomastiamale breast tissue •Testosterone treatments Turner’s Syndrome •XO genotype—Monosomy X •1 in 2,500 births •Short, sterile •75% result in non-disjunction from the father Other Chromosomal Mutations Affect many different genes Caused by errors in meiosis or environmental disturbances Translocation – occurs when a piece of one chromosome breaks off and attaches to a nonhomologous chromosome Inversion – occurs when a piece of one chromosome breaks off, flips, and reattaches to the same chromosome Deletion – occurs when a piece of a chromosome breaks off and is lost Duplication – occurs when a segment of a chromosome is repeated XYY-Jacob’s Syndrome a.k.a. “Super Males” • 1 in 1,000 men •Normal appearance, very tall •Low IQ, prone to violence