Single-Nucleotide Polymorphisms (SNPs): Difference between revisions

The order that the SNPs are listed within your raw data file is arbitrary and it is impossible to know which gene came from each parent without comparing the raw data to another relative. If both genes are the same (A A for example) then one A came from mom and one from dad. If your DNA is heterozygous at a certain SNP (C G for example), the only way to know which parent gave you the C and which the G is by comparing against other relatives. Sorting out the paternal and maternal SNPS is called phasing. In this situation, if you compared your DNA against your mom's and at the spot where you have C G, your mom has G G then you must have inherited the C from your dad and the G from your mom. If you are C G and your mom is also C G, then it is still unclear which gene came from which parent and comparing against your dad or another relative would be necessary to figure it out. Programs such as GedMatch.com offer the ability to phase your DNA by comparing it against one or both parents. Using phased kits reduces the amount of false segments identified between you and a match and is a valuable tool for people interested in small DNA segments. However, in cases where you and the parent being compared against are both heterozygous (like C G) the value becomes a no call and is discarded from the comparison. For this reason, comparing your DNA against both parents creates better results than just comparing against one. Perhaps in the spot where you and your mom are both C G, your father is C C, now it can be concluded you inherited the C from your father and the G from your mother.