PEDIGREE CHARTS

A family history of genetics

Edited from the original produced by Paul Billiet[http://www.saburchill.com/IBbiology/bio_hp.html]

What is a pedigree chart?

a diagram that shows the appearance of a particular gene from one generation to the next

can be used to study the inheritance of a hereditary condition (like cystic fibrosis)

are particularly useful when there are large families and a good family record over several generations.

Symbols Used in Pedigree Charts

A solid square or circle indicates that the person has a certain trait

A marriage with five children, two daughters and three sons.

Oldest child Youngest child

male female

Vertical lines connect children to their parents

A half-filled square or circle indicates that the person is a carrier of the trait.

Organizing the Pedigree Chart

A pedigree chart of a family showing 20 individuals

Organizing the Pedigree Chart

Generations are identified by Roman numerals

I

II

III

IV

Organizing the Pedigree Chart Individuals in each generation are identified by Arabic numerals numbered from the left

I

II

III

IV

21 3 4 5 6 7

4321 65

54321

21

Organizing the Pedigree Chart In this example, let’s look at a recessive trait like light eyes.

I

II

III

IV

21 3 4 5 6 7

4321 65

54321

21

Individuals II3, II6, IV2, and IV3 have light eyes.

The carriers (of the recessive gene) are I1, I2, III5, and III6.