What is a Pedigree Chart?
• Definition: Pedigree
chart is a diagram that shows the presence or absence of a trait in a family
over several generations.
•
It
is widely used to track genetic diseases or traits over generations
This is a simplified video that will help you to improve your understanding and problem solving skills in pedigree analysis
Common symbols are the following
1 Y-Linked
Inheritance
•
Y
chromosome passed from father to son.
•
Affected
men pass the trait to all sons
•
Daughters
are not affected
•
The
trait doesn’t skip generations
•
Hairy
ears, Retinitis Pigmentosa.
2 X-Linked
Dominant Traits
More in
Females than males
a) If father
is affected
•
No
male to male transmission
•
All
daughters of affected father are affected
b) If mother
is affected
•
Both
Daughters & sons are affected (50%)
•
The
trait doesn’t skip generations
•
Fragile
X syndrome
3 X-Linked
Recessive Disorder
More in
males than females
a) If father
is affected
•
No
male to male transmission
•
All
daughters becomes carriers
b) If mother
is carrier
•
¼
Affected son and carrier daughter
b) If mother
is affected
•
All
sons become affected
•
The
trait skips one or more generations
•
Hemophilia, Fabry
disease
4 Autosomal Dominant
Disorder
•
Affected
children born to affected parent
•
Both
males and females are affected in equal frequency
•
50%
children affected from affected parents
•
The
trait doesn’t skip generations
•
Huntington
disease, Marfan syndrome, polydactyly, Neurofibromatosis type 1,
achondroplasia
5 Autosomal
Recessive Disorder
•
Affected
children born to affected or carrier parent
•
Both
males and females are affected in equal frequency
•
If
both parents are carriers (heterozygous), ¼ children gets affected
•
The
trait often skip generations
•
More
likely to appear in progeny of related individuals
• cystic fibrosis, sickle cell disease