A haplogroup pertains to a set of haplotypes that share a common ancestor due to a single-nucleotide polymorphism (SNP) mutation. Specifically, haplogroups are made up of neighboring chromosomal positions' allele combinations that are closely linked and tend to be inherited together.
A haplotype refers to a collection of alleles inherited together from a single parent in an organism.
In humans, the majority of the genome is inherited from both parents, and recombination during the process "mixes" the two parental genotypes. Consequently, haplotype combinations are not preserved for many generations, and haplogroups are not well-defined. However, the Y chromosome and mitochondria (mtDNA) are inherited without recombination, with the former passed from father to son and the latter from mother to offspring of both sexes. Hence, we can trace extended haplogroups that remain conserved across many generations and change only due to random mutations.
In the Y chromosome, haplogroups trace the patrilineal line of descent, while haplogroups in mitochondria trace the matrilineal line of descent.
As haplogroups are composed of similar haplotypes, it is often possible to predict a haplogroup from haplotypes. Every haplogroup stems from a single preceding haplogroup (or paragroup) and remains a part of it. Therefore, any related group of haplogroups can be modeled precisely as a nested hierarchy, with each haplogroup set also serving as a subset of a more comprehensive set. This is in contrast to biparental models such as human family trees.
Haplogroups extend from the most recent common ancestor (MRCA) to all subsequent descendants. The oldest haplogroup is Y-haplogroup A00, estimated as 338 thousand years ago.[1]
Haplogroups are a useful tool to locate and date the rise of new populations. A few original founders can be identified by comparing the DNA analysis of multiple, seemingly unrelated, descendants[2].
Genesis and variation of haplogroups
Most of the human DNA is inherited from both parents equally. Each person will have 23 chromosomes inherited from the parent, creating 23 pairs of chromosomes with combinations unique to that person. However, the Y chromosome (one of the 46 chromones) and mitochondrial DNA (external to the nucleus, namely in addition to the 23 pairs of the chromosomes) are inherited differently[3].
The unique way the Y chromosome and mitochondrial DNA are inherited is why most haplogroups are found there rather than on the autosomal chromosomes; twenty-two of the chromosome pairs are the same for males and females. The twenty-third pair - the sex chromosomes - is different, with males having an X and Y chromosome and females having two X chromosomes.
The mitochondrial DNA and Y chromosome are being passed down the generations and would change rarely (due to the small number of new mutations that appear when a sperm or egg cell is created). Therefore, one’s mitochondrial DNA will be identical to that of their mother's. The Y chromosome will, similarly, be inherited from father to son, intact. In other words, a person's Y-DNA or mtDNA is almost identical to that of their direct ancestors a dozen generations ago, up to the rare changes introduced by mutations, and these changes are what allow us to distinguish between haplogroup sub-clades. Their uniqueness makes them the perfect genetic material for long historical studies. While each person has mitochondrial DNA inherited from their mother, only males will inherit Y chromosome, while females will have two X chromosomes. The stability of mtDNA and Y-DNA allows scientists to link specific geographical areas to unique types of Y-DNA and mtDNA and develop a migration timeline from the appearance of different haplogroups.[4]
Haplogroups and family history
The constant replication of Y-DNA and mitochondrial DNA through multiple generations[5] allows humans to trace their genetic paternal and maternal lineage. Haplogroups and subclades (subgroups) originate in specific geographic regions. The combination of genetic information with genealogical data[6][7], can confirm and expand findings about one's origins[8] and paternal migration across the world over time.
Many diseases have a genetic component.[9] Some haplogroups have shown increased susceptibility or resistance to certain diseases and health conditions, including Alzheimer's[10] and Parkinson's[11]. Consequently, the use of gene therapy[12] is increasing to treat, cure, or prevent disease.
DNA testing variation for genealogy
Multiple forms of DNA tests are commercially available today. Each test analyzes DNA to identify and compare changes in a DNA sequence called "markers" (usually single nucleotide polymorphisms, or SNPs). DNA tests vary by testing purpose, the type of targeted DNA, and the number of markers evaluated.
- Tests to identify paternal and maternal lineage focus on Y-DNA and mtDNA, respectively. The results of the tests indicate an existing haplogroup or, in rare cases, the discovery of a new one.
- Autosomal DNA (atDNA) tests target the 22 non-sex chromosomes inherited from both parents. Many test suppliers, including MyHeritage DNA, elect to use autosomal DNA (atDNA) tests exclusively for their greater application.
Popular DNA matching technology is often produced using an autosomal DNA test. The autosomal test read the autosomal chromosomes. Due to the massive recombination upon conception, the DNA is changing so fast that the probability of no detectable match is reaching nearly 100% for matches farther than a dozen generations apart[13].
Haplogroups, focusing on the Y chromosome and mitochondrial DNA, can trace relationship on a much longer spans, many generations back and from one lineage only unlike the autosomal which finds many close relatives, but can't specify the exact lineage. The disadvantage is that they can only reveal the genetic history across a single lineage in one’s family tree. For example, males can test their Y haplogroup to learn about their paternal great-great-great-grandfather’s genetic origins, or use mt-DNA to learn about their maternal great-grandmother origins, but there is no genomic region that hold information about haplogroups from a maternal grandfather.
Mitochondrial "Eve" and Y chromosome "Adam"
Understanding the way Y chromosome and mitochondrial DNA are being inherited, multiple researchers tried to learn more about the possible "Eve", namely the most recent common female ancestor of all living humans and similarly, the first male, "Adam" whose Y chromosome is the earliest version of all living male humans (note that these “Adam” and “Eve” were not “the first couple” - they are not related, and they only inform us about the basal haplotypes at the Y and mitochondria chromosomes, respectively).
The Haplogroup associated with the Mitochondrial Eve is marked with the letter L and is dated to have occurred more than 500,000 year ago. The haplogroup associated with "Y chromosome Adam" also dates to have lived more than 500,000 years ago, which means both "Adam" and "Eve" were possibly alive in similar periods[14].
Use of haplogroups in population research
Research of peoples and historical research, in general, are using haplogroups as a supporting methodology. For example, it was found that the mtDNA of 40% of Ashkenazi Jews originate from only four ancestral women [2]. The four ancestral women were found in Haplogroups K and N1b[15].
The Druze people, a minority in a few countries in the Middle East, were the topic of another research that examined the Y chromosome and mtDNA showed that the Druze originate from multiple and very diverse lineages[16].
Haplogroups could also teach us how Norse women from today's Orkneys Isles contributed to the colonization of Iceland, among other specific human migration in that era in north-west Europe.[17].
Explore more about DNA
- MyHeritage DNA
- The science behind MyHeritage DNA testing at MyHeritage Knowledge Base
References
- ↑ Mendez, F. L. et al. (2013). An African American paternal lineage adds an extremely ancient root to the human Y chromosome phylogenetic tree. American journal of human genetics, 92(3), 454–459.
- ↑ 2.0 2.1 Behar, D. M., Metspalu, E., Kivisild, T., Achilli, A., Hadid, Y., Tzur, S., Pereira, L., Amorim, A., Quintana-Murci, L., Majamaa, K., Herrnstadt, C., Howell, N., Balanovsky, O., Kutuev, I., Pshenichnov, A., Gurwitz, D., Bonne-Tamir, B., Torroni, A., Villems, R., & Skorecki, K. (2006). The matrilineal ancestry of Ashkenazi Jewry: portrait of a recent founder event. American journal of human genetics, 78(3), 487–497. https://doi.org/10.1086/500307
- ↑ Davidson Institute, B. Elad: "Chromosome Y: Size doesn't matter" (September 1, 2018)
- ↑ Ely, B. (2006) How do researchers trace mitochondrial DNA over centuries? Scientific American magazine. (November 6, 2006)
- ↑ Rasmussen, G. (2022, September 7) mtDNA and YDNA in 2022 [Video]. Legacy Family Tree Webinars.
- ↑ Rasmussen, G. (2022, November 2). Right Place, Right Time, Right Person: Intersections of DNA and Document Evidence [Video]. Legacy Family Tree Webinars.
- ↑ Sykes, B., & Irven, C. (2000). Surnames and the Y chromosome. American journal of human genetics, 66(4), 1417–1419.
- ↑ Rasmussen, G. (2022, October 5.) One Man, Multiple Names: A DNA-Based Case Study [Video]. Legacy Family Tree Webinars.
- ↑ MedlinePlus. Bethesda (MD): National Library of Medicine (US); [updated 2021 May 14]. What are complex or multifactorial disorders.
- ↑ Bettens, K., Sleegers, K., and Van Broeckhoven,C.. Current status on Alzheimer disease molecular genetics: from past, to present, to future, Human Molecular Genetics, Volume 19, Issue R1, 15 April 2010, Pages R4–R11,
- ↑ Latsoudis, H., Spanaki, C., Chlouverakis, G. et al. Mitochondrial DNA polymorphisms and haplogroups in Parkinson’s disease and control individuals with a similar genetic background. J Hum Genet 53, 349–356 (2008).
- ↑ U.S. Food & Drug Administration. (Updated 2022 July 28). How Gene Therapy Can Cure or Treat Diseases.
- ↑ MyHeritage Knowledge Base, Alon Diament Carmel PhD, The World Wide DNA Web. (September 24, 2019)
- ↑ Posth, C., Wißing, C., Kitagawa, K., Pagani, L., van Holstein, L., Racimo, F., Wehrberger, K., Conard, N. J., Kind, C. J., Bocherens, H., & Krause, J. (2017). Deeply divergent archaic mitochondrial genome provides lower time boundary for African gene flow into Neanderthals. Nature communications, 8, 16046. https://doi.org/10.1038/ncomms16046
- ↑ Costa, M., Pereira, J., Pala, M. et al. A substantial prehistoric European ancestry amongst Ashkenazi maternal lineages. Nat Commun 4, 2543 (2013). https://doi.org/10.1038/ncomms3543
- ↑ Weizman Institute, Hayadaan Journal, "Is it possible to provide scientific proof for the hypothesis that certain Jewish men are descendants of priestly families?" (Hebrew), March 31 2009.
- ↑ Krzewińska, M., Bjørnstad, G., Skoglund, P., Olason, P. I., Bill, J., Götherström, A., & Hagelberg, E. (2015). Mitochondrial DNA variation in the Viking age population of Norway. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 370(1660), 20130384. https://doi.org/10.1098/rstb.2013.0384