Tuesday, August 30, 2016

Genealogy and DNA

It’s been crash course time! I have been trying to learn as much as I can about DNA testing as possible. I have a couple distant cousins and a first cousin who have agreed to do DNA tests to find out if we can find out if any or all of the 4 people who have contacted me about the possibility of being related are related thru DNA testing. All of my cousins and a possible cousin who have asked for my help in understanding and deciphering the DNA results.

There is only one company that offers their test worldwide - Family Tree DNA. They're also the only company to charge the same price all over the world.  It is very easy to download your RAW data from them and uploaded it into GEDMatch.com for better comparisons.

Jewish genealogists can't assume that paternal line ancestors have had the same surname for over 300 years, interpreting close and exact matches requires more thought and consideration than would otherwise be the case for other populations. Jewish genealogists needs to  have a knowledge of how the surname relates to their family history and needs to consider each family's geographic origins. The Jewish people, unlike other populations, adopted hereditary surnames relatively recently. Surnames may have changed during emigrations or later to make it easier to get good work (not to sound so Jewish). 

Some families just modified their surname spellings to fit with local norms. Y-DNA and mtDNA can be used to determine the relatedness of individuals at 10 generations. There are as many as 1024 ancestors in the family tree, thus, a Y-DNA test or mtDNA test represents only one individual out of 1024. By testing the Y-chromosome DNA, you and your cousins can recover the linkage along a direct paternal line.

Receiving an exact Y-DNA37, Y-DNA67, or Y-DNA111 match to someone with a different surname isn't a cause for those of Jewish descent. Rather, this is the potential discovery of a branch that some time changed their family name.

We do know that Cohanim belong to the same genetic Y-chromosome lineage: Cohanim Modal Halotype (CMH). The Y Haplogroup classification of the male Y-chromosome is currently used to estimate the population group of the paternal line. They are identified by the letters, A through T. Haplogroups are subdivided into one or more levels, called subsclades, which form a tree. By performing a sequence of SNP tests, the Y-chromosome haplogroup is determined.

Each line on the tree lists a haplogroup or subclade, then one or more SNPs follow on the same line. For a sample to belong to a particular subclade, it must test positive for any one of the SNPs appearing on the line, providing positive results were obtained for its haplogroup and any intervening subclades.

SNPs are indicated by these letters at the beginning:
A, AD, AF, AM or AMM, B, BY, CTS, DC (Dál Cais, an Irish group believed to be descended from Cas), DF, E, F, F* (Fudan; beginning letter F; second letter Haplogroup, i.e. FI is Fudan Haplogroup I), FGC, G, GG, IMS-JST, JFS, K, KHS, KL, KMS, L, M, N, P, Page,  Pages, or PS, PF, PH, PK, PR, S, SA, SK, SUR (Southern Ural), TSC, U, V, VL, Y, YP, YSC, Z, ZP.

A Small Glossary

CentiMorgan (cM): A measurement of how likely a segment of DNA is to recombine from one generation to the next. A single centiMorgan is considered equivalent to a 1% (1/100) chance that a segment of DNA will crossover or recombine within one generation.

Centromere: It's one of the parts of each chromosome. A centromere is a dense area that joins together the two chromatids (arms) of each chromosome.

Genetic cousin: Someone that meets the criteria to be a genetic match in genetic genealogical testing, which may or may not be a known cousin.

Haplogroup: A major branch on either the material or paternal tree of humankind. Haplogroups are associated with early human migrations. Today these are associated with a geographic region or regions.

Mitochondrial DNA (mtDNA): The genetic material found in mitochondria which is passed down from females to both sons and daughters. although on the daughters pass down their mother's mtDNA to their children.

X Chromosome: It is one of the two sex chromosomes and is passed down from mother to child. X is the sex chromosome that is present in both sexes, although, singly in males and doubly in females.

Y Chromosome: The Y chromosome passes down from father to son. Females don't have the Y chromosome. It is passed on through the paternal line, making it valuable for surname based genealogy studies.

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