Download X-Linked Recessive Inheritance Specific Features

Session
5
Medical Genetics
Patterns of
Inheritance
Part 2
J a v a d
F a s a
J a m s h i d i
U n i v e r s i t y
o f
M e d i c a l
S c i e n c e s ,
O c t o b e r
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X-Linked Dominant Inheritance
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X-Linked Dominant Inheritance Specific Features
Affected females are more frequent than affected males
All daughters of a affected male, will be affected
Females are usually less severely affected than males
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X-Linked Recessive Inheritance
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X-Linked Recessive Inheritance Specific Features
The trait or disorder should affect males almost exclusively
Are transmitted through unaffected carrier females to their sons
Male-to-male transmission is not observed
Daughters of affected males are obligate carriers
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X-inactivation (lionization)
Occurs at around 15 to 16 days' gestation, when the embryo
consists of approximately 5000 cells
Normally either of the two X chromosomes can be inactivated in
any particular cell.
Thereafter the same X chromosome is inactivated in all daughter
cells
The inactive X chromosome exists in a condensed form during
interphase (bar body)
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Variable Expression in Heterozygous Females
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Images from: Emery's Elements of Medical Genetics, 14th Edition, by Peter D. Turnpenny and Sian Ellard, (2012)
Females with X-Linked Recessive Disorders
Occasionally a woman might manifest features of an X-linked
recessive trait.
Homozygosity for X-Linked Recessive Disorders
Skewed X-Inactivation
Numerical X-Chromosome Abnormalities
X-Autosome Translocations
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Y-Linked Inheritance
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Y-Linked Inheritance Specific Features
only males are affected.
An affected male transmits Y-linked traits to all of
his sons but to none of his daughters.
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Mitochondrial Inheritance
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Mitochondrial Inheritance
Each cell contains thousands of copies of mitochondrial
DNA
Mitochondrial DNA has a higher rate of spontaneous
mutation than nuclear DNA
Mitochondria, and therefore their DNA, are inherited
almost exclusively from the mother
A number of rare disorders with unusual combinations
of neurological and myopathic features
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Mitochondrial Heteroplasmy
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Mitochondrial Inheritance
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Sex Influenced
Autosomal traits that express more frequently in one
sex than in another
Gout and percentile baldness
Hemochromatosis
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Mosaicism
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