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Mutations What Are Mutations? • Changes in the nucleotide sequence of DNA • May occur in somatic cells (aren’t passed to offspring) • May occur in gametes (eggs & sperm) and be passed to offspring Are Mutations Helpful or Harmful? • Mutations happen regularly • Almost all mutations are neutral • Chemicals & UV radiation cause mutations • Mutations can be helpful, harmful, and neutral Types of Mutations Chromosome Mutations • May Involve: – Changing the structure of a chromosome – The loss or gain of part of a chromosome Chromosome Mutations • Five types exist: – Deletion – Inversion – Translocation – Nondisjunction – Duplication Deletion • Due to breakage • A piece of a chromosome is lost Deletions • When a chromosome fragment breaks off and does not rejoin any chromosome. – Cri-du-chat (cry of the cat) Syndrome • Cognitive impairment • Improperly constructed larynx Inversion • Chromosome segment breaks off • Segment flips around backwards • Segment reattaches Duplication • Occurs when a gene sequence is repeated Translocation • Involves two chromosomes that aren’t homologous • Part of one chromosome is transferred to another chromosome Nondisjunction • Failure of chromosomes to separate during meiosis • Causes gamete to have too many or too few chromosomes • Disorders: – Down Syndrome – three 21st chromosomes – Turner Syndrome – single X chromosome – Klinefelter’s Syndrome – XXY chromosomes Down Syndrome • • 90% from egg nondisjunction 10% from sperm nondisjunction • • • Smallish, oval heads IQ well below normal Reduced life span • Risk increases with mothers over 35. Turner’s Syndrome • Only one X chromosome • Called XO • Ovaries don’t develop properly • Short in stature • Brown spots on their bodies Klinefelter Syndrome • • Phenotypically male XXY • • • • • Some breast development Lack of facial hair More feminine figure Tall stature Non-functional testis Chromosome Mutation Animation Gene Mutations • Change in the nucleotide sequence of a gene • May only involve a single nucleotide • May be due to copying errors, chemicals, viruses, etc. Types of Gene Mutations • Include: – Point Mutations – Substitutions – Insertions – Deletions – Frameshift Point Mutation • Change of a single nucleotide • Includes the deletion, insertion, or substitution of ONE nucleotide in a gene Point Mutation • Sickle Cell disease is the result of one nucleotide substitution • Occurs in the hemoglobin gene • These cells clog capillaries, resulting in decreased oxygen supply to brain, tissues. • Lower life expectancy (42, men 48, women) Frameshift Mutation • Inserting or deleting one or more nucleotides • Changes the “reading frame” like changing a sentence • Proteins built incorrectly Gene Mutation Animation FYI Normal Male 2n = 46 25 Normal Female 2n = 46 26 Male, Trisomy 21 (Down’s) 2n = 47 27 Female Down’s Syndrome 2n = 47 28 Klinefelter’s Syndrome 2n = 47 29