Figure 1.

Normal genetic variation in DNA bases. Single nucleotide polymorphisms are normal nucleotide variations inherited from parents. There is a common C allele at a specific site of a gene whereas some individuals carry a variant allele T at that specific site. The individuals in the population will have three genotypes. Person 1 has inherited a C allele from mother (M) at that specific site whereas a C allele from the father (P). Therefore, this person is a C/C homozygote for this specific site. Person 2 has a maternal C and a paternal T and is heterozygote while person 3 carries two variant alleles T (inheriting a maternal T allele and a paternal T allele) at this site and is therefore a “variant homozygote” in the population.