How do you solve pedigree analysis?

How do you solve pedigree analysis?

Skill:

•  Analysis of pedigree charts to deduce the patterns of inheritance of genetic diseases

    
A pedigree is a chart of the genetic history of a family over several generations

  • Males are represented as squares, while females are represented as circles
  • Shaded symbols mean an individual is affected by a condition, while an unshaded symbol means they are unaffected
  • A horizontal line between man and woman represents mating and resulting children are shown as offshoots to this line
  • Generations are labeled with roman numerals and individuals are numbered according to age (oldest on the left)

Determining Autosomal Inheritance

Dominant and recessive disease conditions may be identified only if certain patterns occur (otherwise it cannot be confirmed)

Autosomal Dominant

  • If both parents are affected and an offspring is unaffected, the trait must be dominant (parents are both heterozygous)
  • All affected individuals must have at least one affected parent
  • If both parents are unaffected, all offspring must be unaffected (homozygous recessive)

Autosomal Recessive

  • If both parents are unaffected and an offspring is affected, the trait must be recessive (parents are heterozygous carriers)
  • If both parents show a trait, all offspring must also exhibit the trait (homozygous recessive)

Determining X-Linked Inheritance

It is not possible to confirm sex linkage from pedigree charts, as autosomal traits could potentially generate the same results

  • However certain trends can be used to confirm that a trait is not X-linked dominant or recessive

X-linked Dominant

  • If a male shows a trait, so too must all daughters as well as his mother
  • An unaffected mother cannot have affected sons (or an affected father)
  • X-linked dominant traits tend to be more common in females (this is not sufficient evidence though)


X-linked Recessive

  • If a female shows a trait, so too must all sons as well as her father
  • An unaffected mother can have affected sons if she is a carrier (heterozygous)
  • X-linked recessive traits tend to be more common in males (this is not sufficient evidence though)

Determining Inheritance from Pedigree Charts

How do you solve pedigree analysis?

Pedigree Analysis – With Tricks to Solve Different Pedigree 

Human genome is very complex and it is not possible to obtain the expected 3:1 ration in inheritance pattern. Therefore, we use pedigree analysis to study inheritance pattern in humans. A pedigree is a pictorial representation of a family history, essentially a family tree that outlines the inheritance of one or more characteristics.

In this video, I have explained six types of inheritance patterns and how to identify them with simple tricks and tips.

  1. Autosomal Dominant – affected individual will always have at least one affected parent.
  2. Autosomal Recessive – affected individual will have unaffected parents and skipping of generation.
  3. X-Linked Dominant – affected father – all the daughters will be affected and no skipping of generation.
  4. X-Linked Recessive – affected mother – all the sons are affected, criss cross inheritance – grandfather to carrier daughter to grandson.
  5. Y-Linked Traits – affected father – only sons will be affected.
  6. Maternal Inheritance – affected mother – all the offsprings affected and affected father – none of the offsprings affected.

00:41 Introduction

06:32 Autosomal Dominant

09:42 Autosomal Recessive

13:12 X-Linked Dominant

16:43 X-Linked Recessive

21:04 Y-Linked Traits

22:14 Maternal Inheritance

24:08 Tips and Tricks for solving any type of pedigree analysis

26:53 Examples of how to solve pedigree using these tips

Read more on this topic from a book, Modern Genetic Analysis by Anthony JF Griffiths, William M Gelbart, Jeffrey H Miller, and Richard C Lewontin here. 

Learn more about Homozygous, Heterozygous and Hemizygous – What is the Difference?

How is pedigree analysis calculated?

Reading a pedigree.
Determine whether the trait is dominant or recessive. If the trait is dominant, one of the parents must have the trait. ... .
Determine if the chart shows an autosomal or sex-linked (usually X-linked) trait. For example, in X-linked recessive traits, males are much more commonly affected than females..

What is pedigree analysis explain with example?

A chart which displays the affected members of a family by genetic diseases in the form of a family tree is called pedigree chart. The study of such a chart to detect genetic diseases in a family is called pedigree analysis. The diagram gives some common symbols in pedigree analysis.