MUTATIONS  Several things can go wrong when DNA replicates.  Mutations are when changes occur that affect the sequence of nitrogenous bases in DNA.  There are two major types of mutations: gene mutations and chromosomal mutations.

Gene Mutations  Result from changes in a single gene.  Can be caused by naturally occurring, random events or by factors in the environment.

Gene Mutations  Can be compared with an error in a sentence.  Example: THE CAT ATE THE RAT  Error: THE CAT ATE THE BAT  The sentences both make sense, but the overall meaning has changed.

Point Mutation  A mutation involving a change in a single base is referred to as a point mutation.  The effects can sometimes be minimal and sometimes be severe.  Example: sickle-cell anemia is caused by a point mutation.

Frameshift mutation  Another type of gene mutation  It is where a base is added or deleted  Example: THE CAT ATE THE RAT  Error: THE CAT ATE THE AT

Chromosomal Mutations  Involve changes in an entire chromosome: in the number of chromosomes or in their structure  Like gene mutations, can be caused by either naturally occurring, random events or by factors in the environment.

Nondisjunction  When chromosomes fail to separate correctly during the production of gametes.  Can lead to abnormalities in offspring, with one receiving more than one copy of a particular chromosome or no chromosome at all.  Example: Down’s syndrome (Trisomy 21)

Changes to the chromosome structure  Four types: deletion, inversion, translocation, and duplication.  Some can have little impact on an individual; others can cause developmental disorders, physical disabilities, or even death.

Deletion Inversion  Part of a chromosome breaks off during mitosis or meiosis.  Serious mutation that often causes death.  A section of a chromosome breaks off, changes direction, and recombines in the same chromosome.  Not as serious a problem because the genes are still intact on the correct chromosome.

Translocation Duplication  A piece of a broken chromosome combines with a different chromosome.  Many cause serious developmental and physical disabilities in humans.  A section of chromosome is repeated.  Can lead to serious developmental and physical disabilities.

Mutations  Can occur in either somatic (body) or gametes (sex) cells.  If it occurs in somatic cells, they are not passed on to offspring.  If it occurs in gametes, can be passed on to offspring.

Mutations  Some caused by factors in the environment like X-rays and UV radiation from sun.  Some caused by chemicals found in cigarettes and industrial cleaners.  Somatic mutations can often lead to cancer.