From Warren Date: Mon, 25 Aug 2014 17:11:18 +1000 from Kerry FARMER and her Booklet (52 pages including four appendixes, a glossary and index pages). Her website is at www.familyhistoryresearch.com.au and she works at the National Institute for Genealogical Studies on courses for Australian and New Zealand Genealogy. www.genealogicalstudies.com [NOTE: THE ABOVE REFERENCES ARE PARAPHRASED AND EDITED BELOW BY WARREN] ____________________________________________________________________ SNPs: Man 1 GTACCAGACTA Man 2 GTACGAGACTA ↑ SNP Cell sometimes make copying errors (like typos) where a single DNA ‘letter’ is wrongly copied when the new cell’s DNA is created. This is called a SNP (pronounced ‘snip’). SNP stands for Single Nucleotide Polymorphism. In this example, a SNP mutation involves a C (cytosine) in Man 1 (Dad?) to be passed on as a G (guanine) in Man 2 (son). Not too sure if this would apply to all the kids but suggest it would only apply to each son individually when being created and so may be the same as the father in some cases and maybe another SNP in other cases. That would suggest to me that there was a possibility of other SNPs occurring at each creation eh. Some SNPs cause biological differences in health or appearance, but most SNPs lead to no observable differences. SNPs account for 90% of the genetic variation in humans. Because SNPs mutate very slowly (indeed nearly all SNPs have mutated only once in human history), SNPs are useful for long term population studies. Large proportions of the population have the same SNP. So my assumption that perhaps each creation of sons capable of having a different SNP must be totally wrong as mutations occur very slowly. Still …if they do not show on the outside perhaps they are mutating and not telling anyone eh J. STRs: Man 1 GTACTACTACTACTG 3 Repeats Man 2 GTACTACTACTG 2 Repeats Stretches of DNA contain short sequences that repeat several times, with the number of repeats at a given point varying from person to person (Perhaps this is going to be like numerous mutations that I tried to pin on the SNP eh J). The number of repeats is called the allele (anything for a new name eh). Copying errors (mutations) also happen when passing on the number of repeats, so the new cell may add or subtract one or more repeats. In the example above, when Man 1’s DNA is passed on, the mutation causes the allele (repeat count) of three to be passed on as an allele of two. Think of a stutter. If I say ‘Mary had a li-li-little lamb’, because the underlying sentence is recognised, it is possible to identify the sequence and recognise that a repeating syllable was spoken three times. In fact the syllable was repeated one more time than when I say ‘Mary had a li-little lamb’. In the second version, a mutation occurred as I subtracted one from the repeat count. In the first utterance (‘Mary had a li-li-lamb’), we say that the repeating syllable was spoken three times, so the repeat count – or allele – is 3. In the second case (‘Mary has a li-little lamb’), the repeat count (allele) is 2. When an STR mutation occurs on the Y-Chromosome, it adds or subtracts one or more repeats (so it’s allele increases or decreases by that amount). Areas of relatively stable DNA rarely show mutations causing a change of more than one repeat at a time, making these areas useful for studying inherited DNA. We receive our DNA, including SNPs and STRs from out parents, who in turn received their DNA from their parents. The number of our SNPs and STRs that match with another person indicates how closely related we are. Our DNA will be more similar to close relatives and less similar to distant relatives. Because SNP mutations happen so rarely, analysing SNPs can be used to determine deep ancestral roots, going back thousands of years. These are useful in the study of anthropology. Analysing STRs can predict ‘recent’ common ancestors, in the last few hundred years. These are particularly useful for forensics – and in genealogy.