CHAPTER 14 SECTION 1 Mutations

Are mutations good or bad?  Some mutations lead to genetic disorders  Some mutations may cause a beneficial trait  Some mutations are silent  no effect good or bad. Both!!

What is a Mutation?  Mutation  Mutation – a change in the structure or amount of the genetic material in an organism  A change in the DNA  A mutant is an individual whose DNA or chromosomes are different.

What causes mutations?  When DNA replicates, mutations occur accidently.  DNA polymerase and other enzymes catch some mistakes, but not all  Very rare  Mutagens – substances that cause DNA to mutate  Examples: radiation, UV light, chemical toxins

What are the effects of mutations?  Mutations may help, harm, or have no effect.  Depends on where the mutation occurs.  Depends on how much DNA is affected

Types of Mutations Gene Mutations  Affect one gene Chromosome mutations  Affect many genes

Point Mutations  Point Mutation – a change of a single nucleotide OriginalMutated DNACTTCAT RNAGAAGUA Amino acidGluVal

Silent Mutation  Silent Mutation – a mutation that has no effect on a gene’s function  Why is this possible? Because the genetic code is so repetitive Silent Mutation DNA ATG CCT TCG A RNA UAC GGA AGC U Amino acidMet Pro Ser Same AA sequence

Missense Mutation  Missense Mutation – a mutation that causes the codon to code for a different amino acid  AKA – replacement mutation Missense Mutation DNA ATG CCT TCG CAT RNA UAC GGA AGC GUA Amino acidMet Pro Ser Gln

Nonsense Mutation  Nonsense mutation – a mutation that causes a codon to change to a STOP codon  Causes protein synthesis to stop early.  Protein may not function Nonsense Mutation DNA ACG RNA UGC UGA Amino acidStop

Frameshift Mutation  Frameshift Mutation – a mutation that causes a shift in the reading frame.  Reading frame – the sequence of codons from start to finish Frameshift Mutation DNAATG CCA TCG ATG GCC ATC G RNAUAC GGA AGC UAC CGG UAG C Amino acidMet Pro SerMet Ala Ile

Frameshift Mutation  Insertion – adding one or more nucleotides  Deletion – removing one or more nucleotides  What happens to the reading frame if 3 nucleotides are inserted or deleted?

Chromosomal Mutations  Can occur during meiosis (crossing over)  Usually the homologous chromosomes exchange equally  Sometimes…they do not

Chromosomal Mutations  Deletion – a piece of the chromosome is lost  Usually harmful X-rays

Chromosomal Mutations  Duplication – both pieces remain attached to the same homologous chromosome X-rays

Chromosomal Mutations  Inversion – a piece attaches in the opposite direction ABCDEFGHIJKLMNOP X-rays

Chromosomal Mutations  Translocation – a piece ends up on a completely different chromosome X-rays

Chromosomal Mutations  Gene Rearrangement – an entire gene is moved to another location X-rays

Nondisjunction  Nondisjunction – occurs when homologous chromosomes fail to separate  One cell ends up with extra chromosomes  Down syndrome – extra 21 chromosome Aka – trisomy 21

Are mutations heritable?  Mutations are only inherited if the mutation occurs in the gamete (sperm and egg).  If a mutation occurs in one of your skin cell, it can affect you, but not your children.