Pedigree Charts – Lesson Summary

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Learning Objective

In this lesson we will learn how pedigree charts can be used to show the inheritance of genetic conditions between multiple generations.

Learning Outcomes

By the end of this lesson you will be able to:

  • Explain the function of a pedigree chart, describe its layout and the symbols used, and construct a simple pedigree chart from given information.
  • Determine relationships between individuals on a pedigree chart.
  • Determine genotypes for individuals on pedigree charts showing:
  • Autosomal dominant inheritance
  • Autosomal recessive inheritance
  • X-linked dominant inheritance
  • X-linked recessive inheritance
  • Determine the mode of inheritance shown by a pedigree chart.

 
pedigree charts lesson contents

(Image: soupstock, Adobe Stock)

Lesson Topics

1 | Introduction to Pedigree Charts

2 | Representing Individuals on a Pedigree Chart

3 | Representing Relationships on a Pedigree Chart

4 | Pedigree Charts and Modes of Inheritance

5 | Autosomal Dominant Inheritance

6 | Autosomal Recessive Inheritance

7 | X-linked Dominant Inheritance

8 | X-linked Recessive Inheritance

9 | Interpreting Pedigree Charts

10 | Summary

Lesson Summary

  • Pedigree charts (pedigrees) are diagrams that show inheritance – particularly of genetic conditions – over several generations.
  • Males are represented by squares and females are represented by circles.
  • Unaffected individuals are represented by unshaded squares or circles.
  • Affected individuals are represented by shaded squares or circles.
  • Carriers are sometimes represented by half-shaded squares or circles, or with dots inside squares or circles.
  • Parents are connected by horizontal lines and their offspring are connected by vertical lines.
  • All individuals of the same generation will line up on the same row.
  • For pedigree charts showing dominant inheritance, the condition cannot skip generations.
  • For pedigree charts showing recessive inheritance, the condition can skip generations.
  • For pedigree charts showing autosomal inheritance, the condition affects males and females equally.
  • For pedigree charts showing sex-linked inheritance, the condition affects males and females unequally.
  • It is only possible to confirm the mode of inheritance shown by a pedigree chart in certain situations.
  • Dominant and recessive inheritance can be confirmed if certain patterns are present.
  • Autosomal inheritance can be confirmed if certain patterns are present, but X-linked inheritance cannot be confirmed, only ruled out.

 

Autosomal Dominant Inheritance Autosomal Recessive Inheritance
Cannot skip generations.
(Affected individuals must have at least one affected parent.)		 Can skip generations.
(Affected individuals can have unaffected parents.)
Males and females are equally likely to be affected. Males and females are equally likely to be affected.
X-linked Dominant Inheritance X-linked Recessive Inheritance
Cannot skip generations.
(Affected individuals must have at least one affected parent.)		 Can skip generations.
(Affected individuals can have unaffected parents.)
Males and females are not equally likely to be affected.
(Females more likely to be affected.)		 Males and females are not equally likely to be affected.
(Males more likely to be affected.)