Preparation and Analysis of Pedigree Chart

Objective

To study the preparation and analysis of pedigree chart. 

 

Theory

Pedigree analysis was developed to know how genes are passed from parents to their offspring. It was created as a diagram that can illustrate a family tree, the family members, and their individual genetic characteristics. 

Pedigree chart 

  • It is a diagram that illustrates how phenotypes of a specific organism or gene, and their ancestors change from one generation to the next. It is frequently examined in racehorses, humans, and show dogs. A pedigree is a type of representative chart that displays family data as a diagram or "family tree." 
  • Squares are used to indicate males while circles are used to represent females in pedigrees. Building a pedigree requires researching family history because records from earlier generations have been lost to time. 
  • Relationships are indicated as a sequence of lines on a pedigree chart. The parents are connected by a horizontal line, while their children are connected by a vertical line. The children are arranged in their birth order from left to right and joined by a horizontal zip ship line. When there are twin offspring, a triangle connects them. And if an offspring disappears or passes away, its sign will be crossed by a line, while a little triangle is used to represent an unborn child or an abortion. 
  • Roman numerals like I, II, III, and so forth are used to represent each generation, and Arabic numerals are used to represent each member of the same generation (1,2,3 and so on). 
  • If a trait is founded on the principles of Mendelian inheritance, pedigree analysis criteria can tell if it comprises a dominant or recessive pattern of heredity. 
  • When a family member with a genetic condition is discovered, the pedigree is constructed. This person is known as the proband and is symbolised by an arrow in the pedigree diagram. Both yearly and monthly changes are possible. 

Mendelian disorders 

Mendelian disorders are typically caused by a change or mutation in just one gene. These illnesses are inherited according to Mendel's principles of heredity. A family's pattern of Mendelian disorder inheritance can be traced via pedigree analysis. Two categories of Mendelian disorders exist: 

  1.  Sex-linked disorders 
  2. Autosomal disorders 

Sex-linked disorders

  • Sex-linked disorders are the ones which can be due to mutations in genes which might be connected with sex chromosomes i.e., both with X-chromosome or Y-chromosome. 
  • Any defective gene this is inherited through the sex chromosomes are taken into consideration to be intercourse-connected. Sex-connected issues are both dominant or recessive.
  • In dominant inheritance, the defective gene acquired from one of the mother and father is dominant and is able to causing disorder in the offspring even in the presence of a regular allele in the homologous pair this is obtained from the opposite parent. 
  • On the contrary, for an intercourse-connected recessive disorder, the defective gene is recessive and is able to expressing the disorder in someone most effective if she or he inherits recessive defective alleles, one from every parent. 
  • Examples of such disorders would include haemophilia, colour blindness, etc.

Autosomal disorders

  • Autosomal disorders are a sort of problems which might be connected with genes present on autosomes or chromosomes apart from sex chromosomes. 
  • They aren't sex specific. These problems can have an effect on kids of any sex. These problems are both dominant or recessive. In dominant autosomal problems, the defective allele is dominant and expresses the disorder even withinside the presence of a recessive normal allele. 
  • In recessive autosomal disorder, the defective gene is recessive and might express the disorder simplest in homozygous condition, that is, when a character has the equal pair of defective recessive alleles.
  • Hence someone inherits a recessive autosomal disorder simplest if she or he gets the defective allele from both the dad and mom at some point of reproduction. 
  • Examples of such disorders might include thalassemia, sickle cell anaemia, etc.

 

Learning Outcomes 

  • Students understand about pedigree chart. 
  • Students come to know about the different traits and related disorders. 
  • Students understand how to make a pedigree chart for particular autosomal or sex-linked disorders.