Variations in humans is caused by waves of migrations and admixture with indigenous people, presence of racial elements, adaptations to the environment,
isolation, mating patterns and operation of evolutionary forces such as mutations, gene flow, genetic drift, recombination and natural selection. Study of variations are useful to investigate evolutionary relationships, evolutionary history, gender specific (mitochondrial DNA and Y chromosomes) migrations, appreciate the extent of variation in humans, enhance our knowledge on evolutionary forces, susceptibility (BRCA1 and BRCA2 genes increase the risk of breast or ovary cancer) or protection (mutations in CCR5 gene protect against HIV) to diseases and drug responses (P450CYP2CP gene variants and Warfarin drug dose requirements).
The unit of genetic variation is Mendelian or breeding population. Mendelian population is a group of sexually reproducing individuals or individuals having
the potential capability of reproduction and sharing common gene pool. Indian population offer great opportunity to study variation as it is fragmented in caste, tribal, religious and linguistic groups. Though these fragmented populations live side by side for thousands of years but retain their identity by practising
endogamy and also show variation in the rate of microevolution (alteration in frequency of the gene in a population over a period of time). Indian population
show second highest genetic diversity after African population (Tamang and Thangaraj, 2012). As per Cavalli-Sfroza and Bodmer (1971) the occurrence in
the same population of two or more alleles at one locus, each with appreciable frequency is called polymorphism. If the frequency of variation is more than
1% in particular population then it termed as polymorphism and if less than 1% it is labelled as mutation.
Physical anthropology is demarcated into old (before 1951, W. Laskar era) and new physical anthropology (after 1951-S.L.Washburn era). In Laskar’s
era, physical anthropologists described biological parameters (bone, teeth, body build, components of body, growth and development) to understand
their causes. These parameters are still in use for exploring new dimensions.
In new physical anthropology, dermatoglyphics, applications of mathematical models to understand variations, evolutionary theories, evolutionary forces,
adaptation, serology, biochemical genetics, demographic studies, ecological studies, somatoscopic and somatometry studies gained currency. Human
cytogenetics improved our understanding on the evolution and adaptation.
Development of recombinant DNA technology, subsequent sequencing and next generation sequencing brought many tools (restricted fragment
polymorphism, single nucleotide/copy number variations, microsatellites (Variable Number of Tandem Repeats and short tandem repeats), Alu insertion/ deletion polymorphism, haplotypes, haplogroups, and short tandem repeats of mitochondrial and chromosomal DNA (Y chromosome and autosomes) are
extremely used markers to study human variation. In this unit, salient features on genetic markers are described from blood groups to molecular markers