13. Genetic Pedigree TWO
Transcript of 13. Genetic Pedigree TWO
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Pedigree AnalysisTWO
SDK
December 15, 2014
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Learning Objectives
Pattern of Inheritance
Define common terms used in genetic pedigree
What are the goals of pedigree analysis
What a genetic pedigree is
How to draw a human genetic pedigree
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Pattern of inheritance
Pattern of inheritance is broken in to two major parts.Classical mendelian
AutosomalDominant
Recessive
Sex(X)LinkedDominant
Recessive
Non classical----------Mitochondrail
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Terms
Traitcharacteristic of an organism
Genea heredity unit that codes for a trait.
Alleledifferent gene forms
Dominantthe gene that is expressed (shown) whenever it is
present.In this case one of the gene at one loci is defective and this will
disturb(decrease) the action of the other normal gene of the otherchromosome and brought upon abnormal phenotype.
Recessivethe gene that is hidden. It is not expressed unlessa homozygous condition exists for the gene.
In this case also one of the gene at one loci is defective butthis will not disturb(decrease) the action of the othernormal gene of the other chromosome rather other genewill function normally and give a normal phenotype
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Terms
In general the
Dominant Gene : Code for Structural protein
such as receptors, defect in one allele is enough
to produce diseaseRecessive Gene: Code for Functional proteins
such as Enzymes .defect in one allele is do not
produce disease
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Terms
Homozygoustwo identical (same) alleles for agiven trait (TT) also called purebred.
Heterozygoustwo different (opposite) allelesfor a given trait (Tt), also called hybrid.
Gametesexual reproductive cell (sperm &
egg .
Fertilizationthe fusion of two gametes.
Phenotypephysical trait of an organism.
Genotypethe genes present in the cell.
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Remember
Homozygous = AA or aa = purebred
Heterozygous = Aa = hybrid
Dominant = capital letter (A)
Recessive = lower case letter (a)
Genotype = alleles involved (AA, aa, or Aa)
Phenotype = trait expressed (blue or green)
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Goals of Pedigree Analysis
1. Determine the mode of inheritance:1. Dominant
2. Recessive
3. Sex-linked4. Autosomal
5. mitochondrial, maternal effect.
2. Determine the probability of an affected
offspring for a given cross.
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Steps in Pedigree Analysis
1. Analyze whether the pedigree belongs to a
dominant or recessive group.
1. Dominant
a) Affected person must have affected parentsvery generat on w e a ecte
2. Recessive
a) Parents will be not affected
b) There will be skip generations
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Steps in Pedigree Analysis
1. Autosomal . Both boys and girls will be involved.
Dominant Disease must be in multiple generation.
Disease person must have an affected parents.
Male & female are equally affected
Recessive Disease have skip generation.
Disease person must not have an affected parents.
Because autosomes are involved , Male & female are equally affected
2. X-linked
Dominant
Affected male will transmit the character to all daughters but not to sons Affected female will transmit the character to Half sons and Half daughters.
Recessive
No male to male transfer
Affected male will be more than female
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3. X-Linked Recessive Inheritance
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X-Linked Recessive
More males than females are affected
Affected sons are usually born to unaffected mothers,
thus the trait skips generations
A roximatel 1/2 of carrier mothers sons are affected
Affected Father's Genotype Normal Father's Genotype
Xa Y X Y
a a a a
It is never passed from father to son
All daughters of affected fathers are carriers
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Normal
Mother's
Genotype
Carrier
Mother's
GenotypeX XXa XY X XX XY
All daughters carriers,
all sons normal. Half of sons affected, half of daughters carriers.
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X-Linked Recessive Trait
Lesch-Nyhan Syndrome
Duchene Muscular
Dystrophy
Glucose 6 Phosphate
Fabry's Disease
Bruton's Aggamaglobulinemia
Color Blindness
Complete Androgen Insensitivity
Dehydrogenase Deficiency
Hemophilia A and B
Congenital Aqueductal stenosis
(hydrocephalus)
Inherited Nephrogenic Diabetes
Insipidus
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X-Linked Recessive Trait
Characteristics of an X-linked recessive trait
include:
More affected males than affected females
Male transmission through female
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X-Linked Dominant
Both males and females are affected; often more females than
males are affected
Does not skip generations.
Affected sons must have an affected mother; affected
father
Affected fathers will pass the trait on to all their daughters
Affected mothers if heterozygous will pass the trait on to 1/2
of their sons and 1/2 of their daughters
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X-Linked Dominant Inheritance
Affected males transmit the trait to all of their
daughters and none of their sons.
Affected females transmit the trait to half of
their sons and half of their daughters.
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X-Linked Dominant Inheritance
Affected males transmit the trait to all of
their daughters and none of their sons.
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X-Linked Dominant Inheritance
X Linked Hypophosphotemic Rickets.
Focal Dermal Hypoplasia,
Orofaciodigital syndrome.
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Y-Linked Dominant
Only males are affected
It is passed from father to all sons
It does not skip generations
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Y-Linked Inheritance
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Mitochondrial Genes
Trait is inherited from mother only
All children of a mother are at risk to be affected or
carriers.
About 20 000 enes in the human enome are located in
small compartments in the cell called themitochondria.
Why Mitochondrial Genes Are Needed ??
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Mitochondrial Genes The genes found within the mitochondria contain the information that codes
for the production of many of the important enzymes that drive the
biochemical reactions to produce the bodys source of energy(ATP).
The cells in the body, especially in organs such as the brain, heart, muscle,
kidneys and liver, cannot function normally unless they are receiving a
constant supply of energy (ATP)
Faulty mitochondrial genes can result in absence of these enzymes, or
enzymes that are impaired and do not work properly.
This leads to a reduction in the supply of ATP, and may result in problems
with the bodys functions .
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The pattern of inheritance of conditions due to faulty mitochondrial genes is
often calledmaternal inheritance.
This is because a child inherits the great majority of their mitochondria from
their mother through the ova.
Mitochondrial Genes
working gene copy and others containing the faulty gene.
For a condition to develop, the number of mitochondria with the faulty gene
must be above a critical level (the threshold). Such as
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Mitochondrial Genes
Mitochondria are onlyinherited from the mother.
If a female has amitochondrial trait, all of heroffspring inherit it.
If a male has a mitochondrialtra t, none o s o spr ng
inherit it.
If the mother is not affectedbut has the faulty genes, than
Disease will occur dependingup on the levels of faultygenes.
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Mitochondrial Genes
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