Download Mutations

Mutations
Germ Cell vs. Somatic Cell
 Gene Mutation: affects either one nucleotide
or one codon
 Substitution: one nucleotide is replaced with a
different nucleotide resulting in a new codon
 If the new codon codes for same amino acid – no
effect is show. (Silent Mutation)
 If the new codon codes for a different amino acid
or stop codon. (causing mis-sense or non-sense
mutations)
 Ex: Sickle Cell Anemia
 Substitution: Adenine replaced by Thymine in a single codon;
results in a defective form of hemoglobin
Point mutations are small (but significant)
changes.often in a single nucleotide base.
 Frame-shift Mutation: caused by additions and deletions
of one nucleotide; all codons after mutation are grouped
incorrectly
 Mutation at beginning of gene is worse than near the end of
gene
Frame shift mutations result from either addition or deletion
of one or two nucleotide bases. When this occurs the
"reading frame" is changed so that all the codons read after
the mutation are incorrect, even though the bases
themselves may be still present.
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Germ-Cell: occurs in gametes; only affect
offspring
Somatic Cell: affects body cells; only affects
organism
Lethal: causes death; often before birth
(miscarriages)
Chromosome: changes to part or the whole
chromosome; cannot be repaired by enzymes
Deletion: loss of a piece or whole chromosome
Inversion: segment of chromosome breaks off
and reattaches in the reverse order on same
chromosome
Translocation: piece of chromosome breaks off
and reattaches to a nonhomologous
chromosome
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Down’s Syndrome: Trisomy 21; 3rd 21 can
translocate to chromosome 13 (young mothers)
Duplication: part of chromosome attaches to
homologous chromosome giving two copies of
gene on that chromosome
Nondisjunction: failure of a chromosome to
separate from its homologous chromosome
during anaphase of meiosis; one gamete
receives extra copy of chromosome other
gamete does not receive one
 Karyotype: chromosomes are
stained and photographed
under the microscope, cut from
photo and arranged by size
and shape; can detect
chromosomal abnormalities
 Monosomy: a zygote with only
45 chromosomes; one copy of
a chromosome
 Trisomy: three copies of a
chromosome; 47
chromosomes total
 Both result from
nondisjunction
 Trisomy 21
 Mild to severe mental
retardation
 Distinct Facial Features
 Heart Defects
 Fingerprints – Sworl
 Most Common Birth
Defect – 1/700 births
 Mother’s Age over 40 –
1/80
 Problems during
Oogenesis
 Trisomy of sex
chromosomes; XXy
male
 Feminine
Characteristics,
Infertile
 George Washington?
 No Children – Sterile?
 Dental Problems
 Height – Very tall for
generation
 Still Inconclusive
 Monosomy of Sex
Chromosomes;
XO female
 Infertile
 Dwarfism
 Overweight
 Some mental
retardation
 Webbed Neck
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Trisomy 18
Elfin Appearance
Low set ears
Malformation of many
organs – specifically
heart/lungs
 “Blue Babies” due to
lack of oxygen
 90% die within first 6
months
 Trisomy 13
 Cleft Lip and
Palate
 Polydactyl – more
than ten
fingers/toes
 1/6000 births
 Most die within
first year
 “Cat’s Cry”
Syndrome
 Deletion of a
portion of
Chromosome 5
 Mental
Retardation
• Spontaneous Mutations – Occur naturally
within a cell, although at a normally low rate.
• Induced Mutations – caused by a mutagen
introduced into the cell.
• Include:
• Physical - agents that forcibly break nucleotide
sequences and cause changes to one or both
strands of a DNA molecule.
• Chemical – molecules that enter a cell and
induce permanent changes in the DNA.