[Biology Class Notes] on Pedigree Analysis- Genetic History of Family Pdf for Exam

Pedigree Analysis helps to study family histories and inheritance of genes in humans. It is helpful to analyse 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, racehorses, 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 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 zip ship line and are put in their birth order from left to right. In the 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:

Importance of Pedigree Analysis

1. For Human Usage

Human pedigree analysis can be used to establish the probability of a child 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.

2. Animal Husbandry

Pedigree charts are used for tracking the ancestry of animals in 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.

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1. Get a brief understanding of the syllabus

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