Mutations

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Mutations Pg. 212-213
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Mutation

• Mutation a change in the genetic material of a
  cell.
• Not all mutations are harmful
• Mutations in the gametes (germ cells) can be
  passed on to the offspring
• Other mutations affect somatic (body) cells

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Gene Mutations

• Gene mutations occur in individual genes.
• Point mutations affect only one nucleotide.
• substitution
• 2. Frameshift mutations affect all the codons
  after the point mutation
• insertion
• deletion

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Gene Mutations
1. Point mutation
2. Frameshift mutations
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Chromosomal Mutations

• A change in the number or structure of
  chromosomes.
• Nondisjunction not coming apart
• deletion
• duplication
• inversion
• translocation

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What to look for in a Karyotype?
1. Are there 46 chromosomes? 2. Are there 2
identical pairs of each autosome and 2 sex
chromosomes? 3. Are there any rearrangements
between chromosomes or large deletions?
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Down Syndrome( Trisomy 21)

• results from nondisjunction of autosomes 21.
  There is an extra copy of the 21 chromosome.
• In mothers under 30 it occurs about 1 in 1,500
  births, mothers over 45 the incidence rises to 1
  in 16 births.
• effects of Down Syndrome vary greatly from person
  to person but can include mild to severe mental
  retardation, eyes that slant upward, and heart
  defects.

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Down Syndrome
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Kleinfelters (XXY)

• results from nondisjunction of the
  sex-chromosomes.
• Develop as males who are sterile
• often tall and usually do not develop secondary
  sex characteristics such as facial hair, or
  underarm and pubic hair.

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Turner syndrome (XO)

• results from nondisjunction of the
  sex-chromosomes.
• Symptoms include
• short stature
• lack of ovarian development
• webbed neck
• arms that turn out slightly at the elbow
• low hairline in the back of the head

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Prenatal Diagnosis

• Ultrasonography uses high-frequency sound waves
  to produce an image on a monitor. This allows the
  doctor to determine the position of the fetus and
  fetal abnormalities

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Amniocentesis

• Insertion of a needle into the amniotic sac,
  removing some amniotic fluid which contains cells
  from the fetus. The cells are cultured for a few
  days to get enough cells. A Karyotype is then
  prepared to check for chromosomal alterations.
  The cells are also screened for certain chemicals
  that indicate genetic disorders.

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Chorionic Villus Biopsy

• Cells are removed from the placentia surrounding
  the embryo. Results are obtained more quickly
  than by amniocentesis because enough cells are
  obtained without having to culture the cells.
  Studies show that before the 10th week of
  pregnancy limb defects can result.

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