12th Class Biology Principle Of Inheritance And Variation Pedigree Analysis

A pedigree is a systematic listing (either as words or symbols) of the ancestors of a given individual or it may be the "family tree" for a number of individuals.

Pedigree analysis is carried out in order to word off possible diaster due to picking up of harmful genetic defects like dominant polydactyly (extra digits), syndactyly (joined digits) and brachydactyly (short digits), recessive haemophilia, deaf mutism, birth blindness, colour blindness, thalassemia, alkaptonuria, phenylketonuria, sickle cell anaemia attached ear lobes, tongue rolling etc.

Pedigree chart and symbols : It is customary to represent men by squares and women by circles in a chart for study of pedigree analysis. Marriage is indicated by a connecting horizontal line and the children by attachment to a vertical line extending downward from the horizontal line. Individuals having particular characters to be studied are denoted by solid squares or circles while those not having them are indicated by outlines only. Twins are denoted by bifurcating vertical lines.

In such a pedigree analysis a person who is the beginner of the family history is called proband. It is called propositus, if male and poposita, if female. The children of such parents are known as sibs or siblings. So a family is constituted by such parents and their siblings. Sometimes, a very large family is formed as a result of interconnected marriages. Such a circle of large persons interconnected is called Kindred.