● `color{Violet}"Mutation"` is a phenomenon which results in `color{Violet}"alteration of DNA sequences"` and consequently results in changes in the `color{Violet}"genotype"` and the`color{Violet}" phenotype"` of an organism.

● In addition to recombination, mutation is another phenomenon that leads to `color{Violet}"variation in DNA"`.

● One DNA helix runs continuously from one end to the other in each chromatid, in a highly supercoiled form.

● Therefore, `color{Violet}"loss (deletions)"` or `color{Violet}"gain (insertion/duplication)"` of a segment of DNA, result in alteration in chromosomes.

● Since genes are known to be located on chromosomes, alteration in chromosomes results in `color{Violet}"abnormalities or aberrations"`.

● `color{Violet}"Chromosomal aberrations"` are commonly observed in `color{Violet}"cancer cells"`.

● In addition to the above, mutation also arise due to change in a `color{Violet}"single base pair of DNA"`. This is known as `color{Violet}"point mutation"`.

● A classical example of such a mutation is `color{Violet}"sickle cell anemia"`.

● Deletions and insertions of base pairs of DNA, causes `color{Violet}"frame-shift mutations"`.

● The mechanism of mutation is beyond the scope of this discussion, at this level.

● However, there are many `color{Violet}"chemical and physical factors"` that induce mutations. These are referred to as `color{Violet}"mutagens"`.

● `color{Violet}"UV radiations"` can cause mutations in organisms – it is a mutagen.

● The idea that `color{Violet}"disorders are inherited"` has been prevailing in the human society since long.

● This was based on the `color{Violet}"heritability"` of certain characteristic features in families.

● After the rediscovery of Mendel’s work the practice of `color{Violet}"analysing inheritance pattern"` of traits in human beings began.

● Since it is evident that `color{Violet}"control crosses"` that can be performed in pea plant or some other organisms, are `color{Violet}"not possible"` in case of `color{Violet}"human beings"`, study of the `color{Violet}"family history"` about inheritance of a particular trait provides an alternative.

● Such an `color{Violet}"analysis of traits"` in a `color{Violet}"several of generations"` of a family is called the`color{Violet}" pedigree analysis"`.

● In the pedigree analysis the inheritance of a particular trait is represented in the `color{Violet}"family tree"` over generations.

● In `color{Violet}"human genetics"`, pedigree study provides a strong tool, which is utilised to `color{Violet}"trace the inheritance"` of a specific trait, abnormality or disease.

● Some of the important `color{Violet}"standard symbols"` used in the pedigree analysis have been given in the image below:



● Each and every `color{Violet}"feature"` in any organism is controlled by one or the other `color{Violet}"gene located on the DNA"` present in the chromosome.

● DNA is the `color{Violet}"carrier of genetic information"`. It is hence transmitted from one generation to the other without any `color{Violet}"change or alteration"`.

● However, changes or alteration do take place `color{Violet}"occasionally"`.

● Such an alteration or `color{Violet}"change in the genetic material"` is referred to as `color{Violet}"mutation"`.

● A number of `color{Violet}"disorders"` in human beings have been found to be associated with the `color{Violet}"inheritance"` of changed or `color{Violet}"altered"` `color{Violet}"genes or chromosomes"`.