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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-.

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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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