Mutations

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

Mutations happen regularly Can occur during DNA replication Chemicals & radiation can cause mutations Many mutations are repaired by enzymes

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

Types of Mutations

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

Chromosome Mutations Five types exist: Deletion Inversion Translocation Nondisjunction Duplication

Deletion Due to breakage A piece of a chromosome is lost and not replaced

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

Inversion Chromosome segment breaks off Segment flips around backwards and reattaches

Inversion

Duplication Occurs when a gene sequence is repeated

CMT Syndrome Chr.17 duplication Inherited Weakness of foot High arches and hammer toes are common

Translocation Involves two chromosomes Part of one chromosome is transferred to another chromosome

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

Translocation

Nondisjunction Failure of chromosomes to separate during meiosis Causes gamete to have too many or too few chromosomes

Symptoms of Klinefelter Syndrome (XXY)

Gene Mutations Change in the nucleotide sequence of a gene May only involve a single nucleotide May be due to copying errors, chemicals, viruses 20

Point Mutation Change of a single nucleotide Includes the deletion, insertion, or substitution of ONE nucleotide 21

Point Mutation Sickle Cell Anemia is the result of one nucleotide substitution Occurs in the hemoglobin gene 22

Frameshift Mutation Inserting or deleting one or more nucleotides Changes the “reading frame” like changing a sentence Proteins built incorrectly 23

Frameshift Mutation Original: Frame Shift (an “a” is added): The fat cat ate the wee rat Frame Shift (an “a” is added): The fat caa tet hew eer at ?????????????? 24

Amino Acid Sequence Changed 25

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