How Do DNA Segments Get Smaller?

Many genetic genealogists, myself included, often talk about DNA segments getting “broken up” or “broken down” as they are passed from one generation to the next. But this language can be misleading, since DNA isn’t really “broken up” into pieces when it passed down; instead, a few pieces are traded between nonsister chromosomes in a process called RECOMBINATION.

Genetic recombination is a process of crossover between chromosomes during MEIOSIS (meiosis = a very specialized cell division that creates eggs and sperm for reproduction). Very early in meiosis, the cells duplicate the chromosomes. Normally, every cell has 23 pairs of chromosomes, for a total of 46 chromosomes. However, in the first step of meiosis, the chromosomes are duplicated to result in a total of 92 chromosomes. There are 4 copies of chromosome 1 (2 copies of the chromosome you got from your mother, and 2 copies of the chromosome you got from your father). There are 4 copies of chromosome 2, and so on.

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Announcing the Genetic Genealogy Standards

Today, at the first annual Salt Lake Institute of Genealogy Colloquium, the final draft of the Genetic Genealogy Standards were officially announced and released!

The standards are the work of a wonderful group of people, and have been in the works for over a year (see “DNA Standards and Certification – A Response to an NGS Quarterly Editorial” and “Announcing the Creation of Genetic Genealogy Standards“). Thanks in large part to a very productive comment period in May and June of 2013 in which more than 75 comments were provided, the document has been fine-tuned and we believe it is an excellent source of guidelines.

There will be lots more to come, including guidelines for Y-DNA and mtDNA testing and interpretation, as well as some guidance for citing DNA test results in reports, scholarship, and in general. Stay Tuned!

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