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Pedigree Analysis and Mutation

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Pedigree Analysis and Mutation - Lesson Summary

A hereditary disorder is a condition that is genetically passed on to one’s offspring. Due to certain scientific and ethical reasons, it was not possible to carry out controlled crosses in human beings, the only alternative was to study a family’s history to understand the inheritance of a particular trait.
Such a genetic analysis of a trait that is traced through several generations of a family is known as pedigree analysis. This analysis plays a very important role in tracing the inheritance of abnormal traits. A pedigree analysis involves using a pedigree chart with standard symbols to represent the inheritance of a particular trait. The standard symbol representing a male is a square and that for a female is a circle. A rhombus is used in case the sex is unspecified, and a filled square, circle or rhombus is used to represent an affected individual. A heterozygous male is represented by a half-filled square and a heterozygous female by a half-filled circle. A circle with a dot in the centre represents a carrier. Pedigree analysis helps trace alterations in genes.
It is the genes in the DNA helix of a chromosome that contain information regarding inheritance.
Mutation in genetic material leads to changes in the genotype and phenotype of an organism. Mutations in the genetic material can be of two types – gene mutation and chromosomal mutation. Further, gene mutations can be of different types, such as substitution, deletion and insertion. In substitution mutation, normal base pairs of DNA are substituted by other base pairs. A type of substitution mutation is point mutation, where a single base pair of DNA is substituted by another base pair. Insertions occur when a sequence in a gene is added. However, when deletions and insertions of several base pairs of DNA occur, it results in a frame-shift mutation.
Unlike gene mutations, chromosomal mutations occur when the number of chromosomes changes or when there is a change in the structure of a chromosome. Chromosomal mutations can occur during the formation of a zygote, which can lead to an increase or a decrease in the chromosomal number or structure. Down’s Syndrome and Jacobsen’s Syndrome are some disorders caused by chromosomal mutations.
There are several physical and chemical factors that change the genetic structure or that induce mutations. These factors are known as mutagens. UV radiation, gamma rays, alpha particles, bromine and nitrous acid are some mutagens that cause changes in the genetic structure. Therefore, mutations in genes and chromosomes lead to several disorders and the inheritance pattern of these disorders can be studied through pedigree analysis.


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