Biology MUTATION AND PEDIGREE ANALYSIS

### KEY TOPICS

star Mutation
star Pedigree Analysis

### MUTATION

● 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 thecolor{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.

### PEDIGREE ANALYSIS

● 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 thecolor{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".