Download Genetics

3/29/2008
What Do You Know
Genetics
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What is a chromosome?
How many chromosomes do we have?
Where are chromosomes located?
What is a gene?
And genetic abnormalities
Definitions
• Cell: Building blocks of the human body,
approximately 50 trillion of them
• Cell nucleus: brain of the cell, it makes
amino acids that form proteins
• Chromosome: strands of DNA
(deoxyribonucleic acid contained in the
nucleus of every cell, a map of how to
make amino acids
Definitions
Chromosomes
• 22 pairs in each somatic cell
• 1 pair of sex chromosomes (X and Y) for a
total of 23 pairs in each cell
• 23 iindividual
di id l chromosomes
h
iin ovum and
d
sperm
T with A, G with C
• Nucleotide: DNA building block containing
one of four bases, adenine (A), thymine
(T) guanine (G), or cytosine (C)
• Codon: a series of three bases in
succession, several codons make a gene.
• A gene is a series of codons that
determine a human trait (phenotype)
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Start and stop sequence
• Start in gene = TAC in DNA
• Stop in gene = ATT, or ATC or ACT
Chromosome duplication
• Unravel
• Separate
– Still connected at the centromere
– Short
Sh t arm, long
l
arm
– Rna cmake cope, goes to ribosome to
manufacture
– Copy comes back to nucleus
– Separation occurs
Definitions
• Locus – the location on the chromosome
where the gene resides
• Alleles – two genes that control the same
characteristic
• Dominant – The allele that takes
precedence
• Recessive – The gene that takes a back
seat
How Severe? It Depends
• Penetrance – the clinical appearance of a
defect
• Expressivity – The severity of the clinical
appearance
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Genetic defects
• Gross abnormalities – dysjunction during
meiosis or a major break
• Genetic inheritance – dominant or
recessive traits
• Genetic abnormality – gene disruption at
the molecular level
Gross Chromosomal Abnormalities
• Trisomy 21 (Down Syndrome)
– During meiosis, chromosome 21 does not
divide evenly resulting in an extra
chromosome
Autosomal Dominant Inheritance
Down Syndrome
• More frequent in women over
40
• Impaired cognitive ability
• Enlarged
E l
d epicanthic
i
thi ffold
ld
• Protruding tongue
• Excessive saliva, fissured
tongue
• Severe periodontal disease
Autosomal recessive inheritance
Sex (x) linked recessive
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Meiosis
Autosomal Dominant oral conditions
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Ectodermal dysplasia
Partial anodontia
Tori (palate and mandibular)
Maxillary exostosis
Cyclic
y
neutropenia
p
Papillon Lefevre syndrome
Gingival fibromatosis
Cherubism
Cleidocranial Dysplasia
Gardner Syndrome
Isolated cleft lip with/without cleft palate
Ectodermal Dysplasia
• Partial or complete
anodontia
Ectodermal Dysplasia
• Autosomal Dominant
• Thin hair, few sweat
glands, abnormal
fingernails,
g
• Prominent frontal
bone, depressed
nose bridging
Pegged or missing maxillary lateral incisors
• Autosomal dominent
• 1-3 % of population
• 20% have missing
premolars (usually
mandibular 1st)
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Torus Palatinus
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Mandibular Tori
• Autosomal dominant
• Variable expressivity
• Marked penetrance
Cyclic Neutropenia
• Periodic decrease in
neutrophil production
and maturity
• Mild to severe oral
conditions
Autosomal dominant
Variable expressivity
Marked penetrance
Female and Native
American predilection
Exostosis
• Autosomal dominant
• Tori on buccal aspect
of maxilla
• Compact bone only
• symptomless
Peutz-Jeghers syndrome
• Autosomal dominant
• Characterized by
pigmentation around eyes,
nose and mouth
• Associated gastrointestinal
polyps
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White Sponge Nevus
• Autosomal dominant trait
• White corrugated appearance
• Can be confused with
leukoplakia
• Appears
A
early
l iin childhood
hildh d
Amelogenesis imperfecta
• No associated systemic abnormalities
• Four types,
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Type I - hypoplastic
Type ll - hypocalcified
Type lll - hypomaturation
Type lV - hypoplastic-hypomaturation
cherubism
• Autosomal
dominance with
marked penetrance
• Enlargment of
facial bones
• Begins early in life
AI hypoplastic
• May be autosmmal
dominant or recessive
• Random pits or no
enamel at all
• Can be autosomal dominant, autosomal recessive,
or x linked recessive
Ai hypocalcified
• May be autosomal dominant or recessive
• Enamel has normal thickness but is not
calcified
Ai Hypomaturation
• X linked recessive
• Normal thickness and
hardness but white
appearance
pp
• Also called snow
capped
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AI – hypoplastic - hypomaturation
• White enamel with
pits
Dentinogenesis imperfecta
• Autosomal dominant
• Imperfect dentin
causes bluish color
• Roots are blunted,
sclerotic pulp canals
• Enamel chips
because it is not
supported.
Papillon-Lefevre Syndrome
• Autosomal recessive
• Hyperkeratosis of palms
and feet
• Destruction of
periodontal tissues at an
early age, continues with
permanent dentition
• Early loss of teeth
• Can you identify
the types?
Gardner’s syndrome
• Autosomal dominant
• Numerous intestinal
polyps that become
cancerous
• Associated osteomas and
odontomas in mandible
and maxilla
Gingival fibromatosis
• Autosomal dominant
• Associated with
several genetic
syndromes
y
• Tissue very firm, pale
in color
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Cleidocranial dysplasia
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Autosomal dominant
Absence of clavicles
Pronounced forehead
Multiple supernumerary
t th
teeth
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