Mutations 2011 (PowerPoint)

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					 Mutations
Mutations are defined as “a sudden
 genetic change in the DNA sequence
 that affects genetic information”.
They can occur at the molecular level
 (genes) and change a single gene, or at
 the chromosome level and affect many
 genes.
Things that can cause mutations are
 called “mutagens”.
Known mutagens are ultraviolet light,
 cigarette smoking, certain chemicals
 like PCB’s.
 Effects of Mutations
Silent mutations - have no effect on the
 expression of the gene.
 Causes for this type of mutation:
   It is in a non-coding region
   It does not change the amino acid sequence
   The change does not affect the folding of the
    protein
Inheritability of Mutations
 It depends on where it occurs
 i. Germ mutations – occur in gametes.
      Inheritable (colorblindness, hemophilia)
 ii. Somatic mutations – affect body cell, not
      inheritable (cancer)
Types of Mutations – mistakes

   a) Gene (point) Mutations – effects a
      single gene
          i. Substitution
          ii. Frameshift
   a) Chromosomal mutations – most
      drastic, change in structure or # of
      chromosomes (affects many genes)
III.    Point Mutations

       a) Substitution – one base exchanges
          for another, affects 1 amino acid
          (Ex. GCA-TCA  GCT-TCA
12.                                Mutations
4
The Effects of Point Mutations
 ►A point mutation is a change in a single base pair in DNA.
       A change in a single nitrogenous base can change the entire structure
        of a protein because a change in a single amino acid can affect the
        shape of the protein. (SUBSTITUTION)


          mRNA
Normal
          Protein
                                                                        Stop
                                                 Replace G with A



 Point mRNA
mutation Protein
                                                                        Stop
Effects of substitution mutations
Missense mutations – causes a
 change in the amino acid coded for
Nonsense mutations – causes a stop
 codon to occur prematurely
a) Frameshift – affects several amino
   acids
       -Insertion – 1 base is inserted,
       affects several amino acids
       Ex. (GCA-TCA  GCA-GTC-A
       -Deletion – base is removed, affects
       several amino acids
       Ex. (GCA-TCA  GCT-CA
12.                                 Mutations
4
 Frameshift Mutations
 ►What would happen if a single base were lost from a DNA
  strand?
 ►A mutation in which a single base is added or deleted from
  DNA is called a frameshift mutation because it shifts the
  reading of codons by one base.
       As a result, every codon after the deleted base would be different.

                                           Deletion of U




                                                                         mRNA

                                                                         Protein
Chromosome mutations
 Nondisjunction – incomplete
  chromosome division during
  meiosis; results in gametes
  with too many or too few
  chromosomes.
 Ex: Down syndrome is caused
  by an extra #21 chromosome
Polyploidy   Aneuploidy
Down’s Syndrome
     •Trisomy 21
     •1 in 700 births
     •Mental
     retardation
     •Males are sterile
     but females are
     not
Complete the back side
For the lab
 Each person needs
   A lab sheet
 Each group (2 people) needs
     A sheet of butcher paper
     A DNA sequence (goldenrod)
     mRNA nucleotides (multiple colors on the back counter)
     tRNA’s (multiple colors on the back right table)
     Scissors
     Tape
     Markers
 All other supplies can be found in the beige trays in the back

 You will turn in the butcher paper for a grade
   The next slide will show you what the butcher paper should look
    like
Label the following:
CODON
ANTICODON                     DNA Strand
mRNA
DNA
Ribosome                                          NUCLEUS
RNA Polymerase
                                                CYTOPLASM
Purine
Pyrimidine
DNA nucleotide
RNA nucleotide         tRNA’s + amino acid sequence
Phosphodiester bond
Hydrogen bond
Peptide bond                  mRNA Strand
Likelihood of chromosomal
mutations
1 in 1700 for mothers <
 20.
1 in 1400 for mothers
 >20<30.
1 in 750 for mothers
 >30<35.
1 in 16 for mothers >45.
Sex chromosome disorders –
 occurs as a result of nondisjunction
 of the sex chromosomes
Ex: Turner’s syndrome – X-;
 Klinefelter’s syndrome – XXY.
    Klinefelter’s Syndrome
•XXY
•1 in 1,000
•Usually sterile because of
low sperm count
•Tall, sparse body hair
•Suffer from gynecomastia-
male breast tissue
•Testosterone treatments
       Turner’s Syndrome
•XO genotype—Monosomy X
•1 in 2,500 births
•Short, sterile
•75% result in non-disjunction
from the father
Other Chromosomal Mutations
 Affect many different genes
 Caused by errors in meiosis or environmental
  disturbances
Translocation – occurs when a
 piece of one chromosome
 breaks off and attaches to a
 nonhomologous chromosome
Inversion – occurs when a
 piece of one chromosome
 breaks off, flips, and reattaches
 to the same chromosome
Deletion – occurs when a
 piece of a chromosome
 breaks off and is lost
Duplication – occurs when
 a segment of a
 chromosome is repeated
    XYY-Jacob’s Syndrome a.k.a.
    “Super Males”
• 1 in 1,000 men
•Normal appearance, very
tall
•Low IQ, prone to
violence
   Patau’s Syndrome
•1 out of 6,000 births
•Trisomy 13
•80-90% do not survive past 1 yr old
   Edward’s Syndrome
•Trisomy 18
•Second most common
trisomy after down’s
syndrome
•Only 5% live to age 1
•1 out of 8,000 births
•Severely retarded, many
die from malformed heart
•Polydactyly or syndactyly
   Cri du Chat
•“ Cry of the Cat”
•1 in 50,000 births
•Severe mental
retardation
•Low mortality rate

				
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