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Chapter 14 Sec 1: Genes in Action Mutation: The Basis of Genetic Change • The change in the structure or amount of the genetic material of an organism Mutant • An individual whose DNA or chromosomes differ from a previous or normal state. Evolution • Genetic differences among organisms originate as some kind of genetic mutation Causes of Mutation • Occur naturally as accidental changes to DNA or to chromosomes during the cell cycle – Mutagens: environmental factors like radiation & some chemicals Effects of Mutation • A small change in the DNA can affect one amino acid in a protein – Only noticed if they cause a disease Kinds of Mutations • Different kinds of mutations are recognized as either changes in DNA or changes in the results of genes Mutations as Changes in DNA Point Mutation • Change of a single nucleotide in a sequence from one kind of base to another Insertion or Deletion • Errors in replication can cause the deletion or insertion of a nucleotide Mutations as Changes in Results of Genes Silent Mutation • It has no effect on a gene’s function – Point mutation Missense Mutation • Results when a codon is changed such that the new codon codes for a different amino acid Frameshift Mutation • Causes the starting point of “reading” the gene to change which translates to different codons Nonsense Mutation • Results when a codon is changed to a STOP signal – Protein may fail to function More or Fewer Amino Acids • If the insertion or deletion is a multiple of 3, reading will be preserved • Protein will have fewer amino acids Chromosomal Mutations At a chromosome level • In eukaryotic cells, the process of meiosis creates the chance of mutations at the chromosome level Deletion • Occurs when a piece of chromosome is lost Duplication • Occurs when a piece remains attached to its homologous chromosome after meiosis Inversion • Occurs when a piece reattaches to its original chromosome, but in a reverse direction Translocation • Occurs when a chromosome piece ends up in a completely different, nonhomologous chromosome Gene Rearrangement • Chromosomal mutation can move an entire gene to a new location • Likely to disrupt the gene’s function Effects of Genetic Change Germ Cell • Mutations in germ cells can be passed on to the next generation Sickle Cell Anemia • Recessive trait • Poor blood circulation, pain, organ damage Tay-Sachs Disease • • • • Recessive trait Deterioration of central nervous system Death in early childhood Caused by defective form of an enzyme Cystic Fibrosis • Recessive trait • Mucus buildup in organs • Difficulty breathing and digesting Hemophilia • Recessive, sex linked • Failure of blood to clot, excessive bleeding and bruising Romanoffs - Hemophilia Pedigree for Hemophilia Huntington Disease • Dominant trait • Gradual deterioration of brain tissue in middle age • Shorter life expectancy Achondroplasia • Homozygous Dominant – Don’t survive • Heterozygous Dominant – Lead normal lives and can reproduce Camptodactyly • Genetic abnormality that affects the shape and movement of fingers • Variation in the phenotype of the trait Examples: Cri-du-chat • Deletion from chromosome 5 resulting in mental retardation and the development of an abnormally shaped larynx Progeria Syndrome • A set of symptoms that characterize a disorder – Hutchinson-Gilford Progeria syndrome: mutated gene that leads to premature aging and reduced life expectancy Progeria Syndrome • Gene mutates at random • Dominant over its normal partner on the homologous chromosome Progeria Syndrome Large-scale genetic change • Can occur by misplacement, recombination, or multiplication of entire chromosomes Nondisjunction • When pairs of chromosomes fail to separate properly Down Syndrome • • • • Extra chromosome 21 Mental retardation Congenital heart defects Shorter limbs Karyotype Turner Syndrome (XO) • Missing one X chromosome • Female in appearance but their sex organs do not develop at puberty and they are sterile • Short stature, broad based neck Turner Syndrome Klinefelters Syndrome (XXY) • Male in appearance and sterile • Taller than average • Usually notice when males don’t develop at puberty Karyotype XYY • Individuals are somewhat taller than average and often have below normal intelligence • Used to think they were prone to violence