Pedigree charts & analysis

This Medicoapps Masterclass discusses about Pedigree Chart Analysis. Various Topics Discussed are given Below

1. What are the Various symbols used in Pedigree Chart Analysis ?
2. Classification of Various Types of Inheritance
3. Pedigree Chart Analysis of Autosomal Dominant Inheritance Pattern
4. Pedigree Chart Analysis of Autosomal Recessive Inheritance Pattern
5. Pedigree Chart Analysis of X Linked Dominant Inheritance Pattern
6. Pedigree Chart Analysis of X Linked Recessive Inheritance Pattern
7. Pedigree Chart Analysis of Y Linked Inheritance Pattern
8. Pedigree Chart Analysis of Mitochondrial Inheritance Pattern

1. Pedigree Charts & Analysis

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Pedigree Analysis
-
Symbols
Normal Male
Affected Male
Unknown Sex
Normal Female
Affected Female
Heterozygous Male
Heterozygous Female
Female Carrier of
X Linked Trait
Deceased Male Deceased Female
Married
Divorced
Consanguineous
Marriage
Monozygotic
Twins
Dizygotic
Twins

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Types of Inheritance
Autosomal
Mitochondrial
Sex Linked
Dominant
Recessive
X Linked
Y Linked
Recessive
Dominant

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Basic Concepts
Genotype
– GENETIC Make up
Phenotype
– Observable Traits
XX X
x
xx
Allele
- Alternative Form of a Gene [One from Each Parent ]
Recessive Trait
Dominant Trait
Phenotype
Expression
Phenotype
Expression
Phenotype
Not Expressed
Phenotype
Not Expressed
X
x
Homozygous
Heterozygous
XX
xx
X
x

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Autosomal Dominant Inheritance
One Allele Enough to Manifest (Heterozygous) Usually one parent affected [Exception – New Mutation ] Vertical Transmission seen Skipping of Generation in case of Incomplete penetrance
Autosomal Inheritance (Dominant or Recessive)
Male = Female

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Autosomal Recessive Inheritance
Both Allele Required to Manifest (Homozygous) Male = Female Consanguineous marriage common Horizontal Transmission seen
Pseudo-Dominance
Case of Autosomal Recessive when a Homozygous marries a heterozygous

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X Linked Dominant
Affected Males Transmit to 100% Female (Because Females Receive it from Father) Male to Male Transmission Never Seen (Because Male Receivesit from Mother) Resembles Autosomal Dominant Pattern of Inheritance

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X Linked Recessive
Males Usually affected and Females usually carriers Affected Males→Carrier Females Knight Move (Diagonal ) Pattern of Inheritance Affected Female only when affected Male marries a carrier fe male [50% Chance Only]
Carrier Females→Affected Males

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Y Linked Inheritance
Affected males transmits to all males Also called holandric inheritance [Only Affects males]
DAZ ( Deleted in Azoospermia) AZF ( Azoospermic Facotr Gene) Mutation causes Azoospermiaor Oligospermia SRY (Sex Reversal Y) codes – Testis Determining Factors (Mutation causes Sex Reversal)

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Mitochondrial Inheritance
Females transmit the Disease to all her Offsprings Mutant Allele present in mitochondrial DNA Also Called CYTOPLASMIC INHERTANCE or Matrilineal Inheritance
Autosomal Dominant (65%) > Autosomal Recessive (25%) > X Linked Recessive (5%)

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Analyzing Pedigree Charts in Exam
Autosomal Dominant Autosomal Recessive
X Linked Dominant X Linked Recessive
Y Linked
Mitochondrial Inheritance
Affected Father Transmits to all Sons
All Children affected of affected Mother
Affected Male Transmits to 100% of Females Knight Move / Diagonal Pattern of Inheritance
Male = Female + Vertical Transmission
Male = Female + Horizontal Transmission

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Brain Teaser
Which Type of Inheritance is Shown in the Pedigree Chart