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Mutations
Germ Cell vs. Somatic Cell
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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
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Point mutations are small (but significant) changes.often in a single nucleotide base.
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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
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
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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
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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
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Trisomy of sex chromosomes; XXy male
Feminine Characteristics, Infertile
George Washington? No Children – Sterile? Dental Problems Height – Very tall for
generation Still Inconclusive
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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
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Trisomy 13 Cleft Lip and
Palate Polydactyl – more
than ten fingers/toes
1/6000 births Most die within
first year
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“Cat’s Cry” Syndrome
Deletion of a portion of Chromosome 5
Mental Retardation
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• 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.