Pedigree Chart:
o It is a pictorial representation of generations of a family showing the information of
family members and their relationship to one another, marriages among cousins
(consanguineous) including details of live births, stillbirths and abortions, etc.
o A pedigree chart shows genetic connections among individuals using standardized
symbols. For drawing pedigree charts certain standard symbols are used).\
o Knowledge of probability and Mendelian patterns are required for understanding the
basis for a trait. Conclusions are most accurate if they are drawn using large number
of pedigrees (generations).
o A sample pedigree chart is presented. According to the mode of transmission the
genetic disorders can be classified as follows:
o Autosomal dominant inheritance
o Autosomal recessive inheritance
o X-linked dominant inheritance
o X-linked recessive inheritance
o Y-linked inheritance and Multifactorial inheritance.
Autosomal Dominant Inheritance:
• The mode of transmission is vertical. An affected person has an affected parent.
• There is 50% of chance of dominant trait being transmitted to off-springs.
• Both males and females are equally affected.
• Dominant gene is expressed in heterozygotes.
• Delayed age of onset.
• The trait appears in every generation without skipping.
• An unaffected offspring does not transmit the disease.
Examples:
– Achondroplasia
, – Angioneurotic edema
– Huntington’s chorea
– Multiple neurofibromatosis
– Osteogenesis imperfecta.
Autosomal Recessive Inheritance:
• Horizontal transmission. The trait appears in sibs and parents are normal.
• History of consanguineous marriage. The parents are blood related. Both the couple are
carriers of abnormal gene.
• 25% chance of having an affected child (double dose of abnormal gene) in a carrier
couple.
• Early age of onset.
• Both males and females have an equal chance of getting affected.
Examples:
– Cystic fibrosis
– Inborn errors of metabolism—albinism, phenylketonuria
– Hemoglobinopathies—sickle-cell anemia, thalassemia.
X-linked Dominant Inheritance:
• Trait is more frequent in females than in males.
• Affected male transmit the trait to all his daughters not to his sons.
• Affected females if homozygote, transmit to all of her children.
• If affected females are heterozygote, transmit the trait to half her children of either sex.
Example:
– Vitamin D-resistant rickets
– Xg blood groups.
X-linked Recessive Inheritance:
o It is a pictorial representation of generations of a family showing the information of
family members and their relationship to one another, marriages among cousins
(consanguineous) including details of live births, stillbirths and abortions, etc.
o A pedigree chart shows genetic connections among individuals using standardized
symbols. For drawing pedigree charts certain standard symbols are used).\
o Knowledge of probability and Mendelian patterns are required for understanding the
basis for a trait. Conclusions are most accurate if they are drawn using large number
of pedigrees (generations).
o A sample pedigree chart is presented. According to the mode of transmission the
genetic disorders can be classified as follows:
o Autosomal dominant inheritance
o Autosomal recessive inheritance
o X-linked dominant inheritance
o X-linked recessive inheritance
o Y-linked inheritance and Multifactorial inheritance.
Autosomal Dominant Inheritance:
• The mode of transmission is vertical. An affected person has an affected parent.
• There is 50% of chance of dominant trait being transmitted to off-springs.
• Both males and females are equally affected.
• Dominant gene is expressed in heterozygotes.
• Delayed age of onset.
• The trait appears in every generation without skipping.
• An unaffected offspring does not transmit the disease.
Examples:
– Achondroplasia
, – Angioneurotic edema
– Huntington’s chorea
– Multiple neurofibromatosis
– Osteogenesis imperfecta.
Autosomal Recessive Inheritance:
• Horizontal transmission. The trait appears in sibs and parents are normal.
• History of consanguineous marriage. The parents are blood related. Both the couple are
carriers of abnormal gene.
• 25% chance of having an affected child (double dose of abnormal gene) in a carrier
couple.
• Early age of onset.
• Both males and females have an equal chance of getting affected.
Examples:
– Cystic fibrosis
– Inborn errors of metabolism—albinism, phenylketonuria
– Hemoglobinopathies—sickle-cell anemia, thalassemia.
X-linked Dominant Inheritance:
• Trait is more frequent in females than in males.
• Affected male transmit the trait to all his daughters not to his sons.
• Affected females if homozygote, transmit to all of her children.
• If affected females are heterozygote, transmit the trait to half her children of either sex.
Example:
– Vitamin D-resistant rickets
– Xg blood groups.
X-linked Recessive Inheritance:
