Pedigree Analysis- Genetic History of Family

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What is Pedigree Analysis?

Pedigree Analysis helps to study family histories  and inheritance of genes in humans. It is helpful to analyze an existing population when progeny data from multiple generations are limited. It helps to study species for a long generation. Scientists are able to find dominant/recessive patterns of inheritance through pedigree charts.

Pedigree Chart

  • It is a diagram which highlights the appearance and occurrence of phenotypes of a particular organism or gene and its ancestors from one generation to another generation. It is analysed commonly in humans, race horses and show dogs. A representative chart that shows the family information in the form of a diagram or “family tree” is called a pedigree. 

  • Pedigrees make use of a standardized set of symbols where squares represent males and circles represent females. Constructing a pedigree means studying family history where earlier generation records are faded with time. 

  • While drawing a pedigree chart, relationships are highlighted as a series of lines. A horizontal line connects the parents and a vertical line leads to their offspring. The offspring are connected by a horizontal zipship line and are put in their birth order from left to right. In case of twin offsprings, they are connected by a triangle. And if an offspring is no more or dies, its symbol will be crossed by a line and if it is still to be born or aborted it is shown by a small triangle.

  • Every generation is denoted by a Roman numeral such as I,II,III and so on and each individual from the same generation is denoted by an Arabic numeral (1,2,3 and so on). 

  • Pedigree analysis rules can determine whether a trait comprises a dominant or recessive pattern of inheritance if it is based on the principles of Mendelian inheritance.

  • Construction of pedigrees is done when a family member is identified who is afflicted with a genetic disorder who is known as the proband and is represented by an arrow in the pedigree diagram.  The changes may occur monthly or yearly.

Symbols Used in Pedigree Analysis

A series of symbols used to represent different aspects of a pedigree are shown as follows:

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Importance of Pedigree Analysis

  1. For Human Usage

Human pedigree analysis can be used to establish the probability of a child for having a particular disorder or condition. It is also used to discover the locations of genes (x, y or autosome chromosome) one needs to know and to determine a dominant or recessive trait. When the answer for a condition appears to be 50:50 between men and women , it is called an autosomal condition and when males are predominantly affected in the pedigree, it is known as x-linked. One of the pedigree analysis examples can be given for an autosomal dominant trait. If at the top of the pedigree, there is a grandmother (individual I-2) who has freckles will be having two of her three children with the trait (individuals II-3 and II-5) and three of her grandchildren have the trait (individuals III-3, III-4, and III-5). 

It is also very important for studying human inherited diseases and the pedigree diagrams make it easier to visualize relationships in families, especially large extended families. Pedigrees often determine the mode of inheritance, i.e. dominant/recessive of genetic diseases.

  1. Animal Husbandry

Pedigree charts are used for tracking the ancestry of animals in the selective animal breeding practices and in livestock for  animals like horses. It also assists in the identification of suitable breeding programs that help in enhancing the desirable traits. Maintaining accurate records of birth and death as well as identifying characteristics of each registered animal is easier through pedigree genetics.

FAQ (Frequently Asked Questions)

1. What does Autosomal mean?

Ans. Autosomal means inherited on chromosome 1-22 and sex-linked means inherited on X or Y chromosomal. An example of autosomal recessive is albinism and PKU. An example of autosomal dominance is Huntington’s disease.

2. What are the characteristics of X-linked recessive Pedigrees?

Ans. In this, trait is rare in pedigree and it skips generations. Therefore, affected fathers don’t pass to their sons and males are more often affected than females. Females are carriers where it is passed from mom to son.

3. What are the characteristics of X-linked dominant Pedigrees?

Ans. Here, trait is commonly seen in pedigree and affected fathers pass to all of their daughters. Males and females can be equally affected. X-linked dominant diseases are rare and often lethal in males and females, eg. skin lesions and X-linked rickets.

4. What are Mitochondrial Genes?

Ans. Mitochondria are only inherited from a mother and if a female possesses a mitochondrial trait, all of her offspring will inherit it. If it’s a male, none of his offspring will inherit it.

5. What are the Dominant and the Recessive Pedigree?

Ans. If two affected people are having an unaffected child, it must be a dominant pedigree where D is the dominant mutant allele and d is recessive wild type allele. Both parents are Dd and the normal child is dd.

If two unaffected people have an affected child, it is a recessive pedigree where R is the dominant wild type allele and r is the recessive mutant allele. Both parents are Rr and the affected child is rr. 

If every affected person has an affected parent, it is a dominant pedigree.

6. How is pedigree analysis helpful for Humans?

Ans. Pedigree analysis will be helpful for humans if individuals wish to be tested if there is a family history of one specific disease or they show symptoms of a genetic disorder or if they are concerned about passing on a genetic problem to their children.