Genetic Mutations

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Genetic Mutations
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Mutations

• Mutations changes in the DNA
• They may not change the individual in a way that
  impacts their reproductive success or
• They can be damaging.
• We dont get to choose which one.
• Mutations can occur mainly in 3 ways
• Spontaneously
• Environmental exposure to mutagens (chemical,
  radiation, etc.)
• Inheritance also called germ line mutations.
  Hereditary mutations occur in the sex cells
  (sometimes referred to as germ cells) and are
  therefore passed on from parent to offspring.

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Genetic Disorders

• A genetic disorder is a disease caused in whole
  or in part by a "variation" (a different form) or
  "mutation" (alteration) of a gene.
• Single gene disorders mutation in a single gene.
  The mutation may be present on one or both
  chromosomes (one chromosome inherited from each
  parent).
• Ex. Sickle cell disease, cystic fibrosis and
  Tay-Sachs disease are examples of single gene
  disorders.
• Chromosome disorders structural changes within
  chromosomes, or excess or deficiency of the genes
  that are located on chromosomes
• Ex. Down syndrome, for example, is caused by an
  extra copy of chromosome 21, but no individual
  gene on the chromosome is abnormal.
• Multifactorial inheritance disorders
  combination of small variations in genes, often
  in concert with environmental factors.
• Ex. Heart disease and most cancers are examples
  of these disorders.

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Gene mutations

• These are mutations within a gene
• A mutation that only changes one nucleotide is
  called a point mutation.
• Substitution
• Insertion
• Deletion
• Resulting proteins can be NOT MADE, NONFUNTIONAL,
  or BETTER FUNCTIONING

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Chromosome Mutation

• The genes location can change on a chromosome
• This is a structural change

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Types of Mutations

• Wild Type Normal ACT-GAA-CTG-ATT
• (Thr-Glu-Leu-Ile)
• Substitution ACT-GAC-CTG-ATT
• (Thr-Asp-Leu-Ile)
• Deletion ACT- - - CTG-ATT
• (Thr-Leu-Ile)
• Insertion ACT-GAA-CCT-GAA-CTG-ATT
• (Thr-Glu-Pro-Gly-Leu-Ile)
• Frameshift ACT-GA-C-TGA-TT
• (Thr-Asp-Stop)
• Inversion ACT-GGT-CAA-ATT
• (Thr-Glu-Gln-Ile)

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Causes of Mutation

• De novo also called new or spontaneous
  mutations, de novo mutations occur in sex cells
  during or after fertilization.
• Somatic also called acquired mutations, these
  happen to individuals in their lifetime. A
  mistake may be made when the DNA is being copied
  to make new cells, or via environmental damage,
  such as UV radiation. Since only somatic (body)
  cells are affected, such mutations cannot be
  inherited.

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Nondisjunction

• Nondisjunction is a chromosome disorder
• It occurs when either homologous chromosomes fail
  to separate during anaphase I of meiosis, or
  sister chromatids fail to separate during
  anaphase II.

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Nondisjunction

• The frequency of nondisjunction is quite high in
  humans, but the results are usually so
  devastating to the growing zygote that
  miscarriage often occurs very early in the
  pregnancy.
• If the individual survives, he or she usually has
  a set of symptoms - a syndrome - caused by the
  abnormal dose of each gene product from that
  chromosome.

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Normal Human Karyotype
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Down syndrome (trisomy 21)(Extra Chromosome 21)

• Down syndrome affects 1700 children
• Characteristic facial features, short stature,
  heart defects, susceptibility to respiratory
  disease, shorter lifespan
• Often sexually underdeveloped and sterile,
  usually some degree of mental retardation.

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Typical Down Syndrome