Pedigree Analysis

Pedigree Analysis
Pedigree Analysis is a tabular representation of a family history by taking a particular disease or character into consideration.

Proband or Propositus is an individual from which a pedigree is initiated.

Female are represented in circles. screenshot-7-copy

Male are represented in squares.screenshot-7

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Individuals carrying the character to be studied are shaded.    screenshot-9-copy or screenshot-8-copy

It helps us to find out whether the gene is dominant or recessive and autosomal or sex-linked. And the chances of expressing itself in the coming generations.

In the case of autosomal genes:
  • It equally affects both males and females.
In the case of sex-linked genes:
  • Affects the males as they are hemizygous.
  • The gene shows criss-cross inheritance i.e., the gene from the father is transferred to the grandson through the daughters.
  • In the case of a sex-linked dominant gene, more females are affected than males.
  • Never transferred from father to son.

In the case of dominant genes:
  • One or both the parents have the disorder.
  • It expresses itself in every generation.
  • The disorder is common in the pedigree.
  • The genotype is either homozygous (BB) or heterozygous (Bb).
  • It affects one-half of the children.
In the case of recessive genes:
  • Neither of the parents may have the disorder.
  • The disorder is rare in the pedigree.
  • Both parents are either heterozygous or homozygous recessive.
  • The disorder skips generations.
  • The genotype is always homozygous (bb).
  • Affected offspring are born to unaffected parents.

 

In the case of Holandric  ( Y-linked) genes:
  •  Affects the males only.
  • Father transfers it to son.
  • It never skips generations.
In the case of Cytoplasmic genes:
  • Gene is inherited from mother.
  • Affected mother transfers the gene to all its offspring.

 

Pedigree 1:

sex-linked recessive

A sex-linked recessive character.

  • It mainly affects the males.
  • The gene skips generation.
  • Criss-cross inheritance is seen.

Pedigree 2:

autosomal dominant

It is an autosomal dominant character.

  • It affects male and female equally.
  • The gene expresses itself in each generation.

Pedigree 3:

autosomal recessive

It is an autosomal recessive character.

  • The gene skips generation.
  • Does not show criss-cross inheritance.

Pedigree 4:

holandric

It is a holandric gene.

  • As it affects only males.
  • The gene is transferred from father to son.

Pedigree 5:

cytoplasmic gene

It is a cytoplasmic gene.

  • Gene is inherited from the mother.
  • As it affects all the offsprings.

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