Pedigree chart

Dr.Rajprasath.RSenior resident

Department of AnatomyJIPMER

Definition

Diagram of family history indicating normal & affected individuals, their

relationship to the proband & their status with respect to a particular

genetic disorder

Symbols used

Mendelian Inheritance

What is inheritance?

• Passage of genes from parents to offspring

• Pair of genes in 23 pairs of chromosomes

• One of pair goes to one gamete Chromosome

Gene

Single gene disorders

• Due to mutation or change in single gene

• Affected gene is passing to the next generation (inheritance)

Types of inheritance

• Based on location & expression of disease

• Autosomal inheritance

• Sex chromosomal inheritance (X-linked)

• Dominant

• Recessive

location

Expression of disease

Expression of disease..

• Dominant – only one gene is affected-disease expressed

• Recessive – disease expressed only if both genes are affected

• Symbols indicating

- Affected gene

- Normal gene

Disease expressed

Dominant

Disease not expressed

Recessive- carrier

Recessive

Disease expressed

/ Dominant

2

3

1

Homozygotes

Heterozygotes

Autosomal inheritance

Autosomal dominant

• One or both of the parents are always affected

• 50% chance of children get affected

• Both sexes are equally affected

• All generations are affected

• Normal children do not transmit the disease

• E.g. Achondroplasia

Marfan’s syndrome

Neurofibroma

Parents

Gametes

Autosomal dominant inheritance

Affected Affected Unaffected

Atconception

How to draw ADPedigree chart

Autosomal recessive

• Parents are healthy carriers

• 25% chance for children getting affected

• E.g. Cystic fibrosis

Phenylketonuria

Sickle cell disease

Tay-sachs disease

Parents

AUTOSOMAL RECESSIVE INHERITANCE

AffectedUnaffected (carrier)Unaffected

Sperm/Eggs

Unaffected (carrier)

How to draw ARPedigree chart

Summary

• What is inheritance?

• Different Modes of inheritance

• How to draw a pedigree chart?

• How to diagnose an inheritance pattern from pedigree chart

• Few points about autosomal inheritance

THANK YOU