Mutations Mutations by huanghengdong



When something goes wrong…
         Causes of Mutations
• Mutations are caused by changes in the
  nucleotide sequence of DNA (A, T, C, G) or of
  a gene (specific area of a chromosome)

• This can occur:
  – During DNA replication
  – During cell division
  – After cell division
            Mutations Types
• Germ-Cell Mutations
  – Occur in an organism’s sex cells
  – Do not affect the organism itself but may be
    passed to offspring
• Somatic-Cell Mutations
  – Take place in an organisms body cells and can
    affect the organism
  – Cannot be inherited
• Lethal Mutations
  – Cause death, often before birth
Gene Mutations
              Gene Mutations
• Point mutations affect a single nucleotide

• Base pair substitutions switches a nucleotide
  – Silent mutation
     • Does not change the amino acid
  – Missence mutation
     • Change of a single amino acid
  – Nonsense mutation
     • Changes amino acid to stop codon
  – Neutral mutation
     • Changes amino acid to chemical similar amino acid
             Gene Mutations
• Frameshift Mutation
  – Change in reading frame due to adding or
    deleting a nucleotide

     • Add A after 2nd nucleotide

        Chromosomal Mutations
• These mutations can be detected by karyotyping

   – Nondisjunction
       • Homologous chromosomes or chromatids don’t split in division
   – Deletion
       • Loss of a piece of chromosome due to breakage
   – Duplication
       • Portion of the chromosome can be duplicated
   – Inversion
       • Part breaks off, then reattaches in reverse position
   – Translocation
       • Part breaks off, reattaches to a non-homologous chromosomes
   – Insertion
       • Extra DNA is inserted into a non-homologous chromosome
         Effects of Mutations
• Always result in changes to genotype (DNA)
  but not always phenotype (what you see!)

  – Neutral
     • No effect

  – Beneficial
     • Enhances fitness

  – Deleterious
     • Decreases fitness
Cystic Fibrosis
                 Cystic Fibrosis
• Genetic disorder affecting the respiratory and
  digestive system caused by defective gene on
  Chromosome 7
   – 1000 different mutations in this gene have been identified
   – Most often caused by deletion of a single amino acid
• Body produces a mucous that clogs the airways and
  increases risks of infection
• Both parents must pass on the gene to their children
   – More than 10 million Americans carry the gene and don’t
     know it
• About 2,500 babies are born with cystic fibrosis in
  the U.S. each year.
Turner Syndrome
           Turner Syndrome
• Caused by missing or incomplete X chromosome
  often due to non-disjunction
• Women with Turner syndrome are usually sterile
  and cannot have children
• Short in stature, stocky appearance, arms that turn
  out slightly at the elbow, receding jaw line, short
  webbed neck, and low hairline
• Affects 60,000 females in the United States. This
  disorder is seen in 1 of every 2000 to 2500 babies
  born, with about 800 new cases diagnosed each year
• In 75-80% of cases, the single X chromosome comes
  from the mother's egg; the father's sperm that
  fertilizes the egg is missing its sex chromosome
Klinefelter Syndrome
         Klinefelter Syndrome
• Caused by an extra X chromosome (XXY) in males
  due to by nondisjuction
• Males are often tall and don’t develop secondary sex
  characteristics (facial hair, underarm hair, etc)
• Often not diagnosed until puberty (less muscular
  body, more breast tissue, less hair) or when men try
  to have children due to sterility
• Treated with hormone replacement therapy –
  testosterone injections
• Klinefelter syndrome is one of the most common
  genetic abnormalities. It affects between 1 in 500 and
  1 in 1,000 males.
Sickle Cell Disease
             Sickle Cell Disease
• Mutation on a gene on chromosome 11 that codes for the
• Blood cells get stuck in the blood vessels and cannot
  transport oxygen, resulting in pain and damage to
  organs, leading to low red blood cell counts
• Both parents must pas a defective gene to their children
• Daily penicillin to prevent infections, folic acid to build
  new cells, blood transfusions, bone marrow transplant
• Unlike normal red blood cells, which can live for 120
  days, sickle-shaped cells live only 10 to 20 days.
• In the United States, the disease most commonly affects
  African-Americans. About 1 out of every 500 African-
  American babies born in the United States has sickle cell

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