Mutations What Are Mutations Changes in the nucleotide

Mutations

What Are Mutations? ØChanges in the nucleotide sequence of DNA ØMay occur in somatic cells, so not passed on to offspring ØMay occur in gametes and be passed on to offspring

ØMutations happen regularly ØCan occur during DNA replication ØChemicals & radiation cause mutations ØMany mutations are repaired by enzymes

Are Mutations Helpful or Harmful? ØMany types of disorders (e. g. skin cancers) result from somatic mutations ØSome mutations may improve an organism’s chances of survival

Types of Mutations

Chromosome Mutations Changing the structure of a chromosome l The loss or gain of part of a chromosome l Ultimately they change either a type of gene l

Chromosome Mutations Ø Five types exist: Deletion l Inversion l Translocation l Nondisjunction l Duplication l

Deletion ØDue to breakage ØA piece of a chromosome is lost and not replaced

Angelman Syndrome Ø Caused by a deletion on a gene (chr. 15) inherited from mother Ø Developmentally delayed Ø Overly happy and excitable

Inversion ØChromosome segment breaks off ØSegment flips around backwards and reattaches

Inversion

Duplication ØOccurs when a gene sequence is repeated

CMT Syndrome ØChr. 17 duplication ØInherited ØWeakness of foot Ø High arches and hammer toes are common

Translocation ØInvolves two chromosomes ØPart of one chromosome is transferred to another chromosome

Translocation

Philadelphia Translocation Ø Part of chr. 8 and chr. 22 go to chr. 9 Ø Individuals develop leukemia Philadelphia Chromosome

Nondisjunction ØFailure of chromosomes to separate during meiosis ØCauses gamete to have too many or too few chromosomes

Symptoms of Klinefelter Syndrome (XXY)

Gene Mutations ØChange in the nucleotide sequence of a gene ØMay only involve a single nucleotide ØMay be due to copying errors, chemicals, viruses

Point Mutation ØChange of a single nucleotide ØIncludes the deletion, insertion, or substitution of ONE nucleotide

Point Mutation ØSickle Cell Anemia is the result of one nucleotide substitution ØOccurs in the hemoglobin gene

Frameshift Mutation ØInserting or deleting one or more nucleotides ØChanges the “reading frame” like changing a sentence ØProteins built incorrectly

Frameshift Mutation ØOriginal: l The fat cat ate the wee rat ØFrame l Shift (an “a” is added): The fat caa tet hew eer at ? ? ? ?

Amino Acid Sequence Changed

Pedigree Analysis Assessing the genetic basis of a disease or trait from its inheritance pattern l Predicting the risk of disease in future offspring in a family (genetic counseling) l