|
Autosomal
Chromosome
pair - one |
Autosomal
Chromosome
pair - two |
Autosomal
Chromosome
pair - three |
Autosomal
Chromosome
pair - four |
|
Autosomal
Chromosome
pair - five |
Autosomal
Chromosome
pair - six |
Autosomal
Chromosome
pair - seven |
Autosomal
Chromosome
pair -
eight |
|
Autosomal
Chromosome
pair - nine |
Autosomal
Chromosome
pair - ten |
Autosomal
Chromosome
pair - eleven |
Autosomal
Chromosome
pair - twelve |
|
Autosomal
Chromosome
pair - thirteen |
Autosomal
Chromosome
pair - fourteen |
Autosomal
Chromosome
pair - fifteen |
Autosomal
Chromosome
pair - sixteen |
|
Autosomal
Chromosome
pair - seventeen |
Autosomal
Chromosome
pair - eighteen |
Autosomal
Chromosome
pair - nineteen |
Autosomal
Chromosome
pair - twenty |
|
Autosomal
Chromosome
pair - twenty-one |
Autosomal
Chromosome
pair - twenty-two |
Sex
chromosome
Chromosome
X |
End of chromosome numbering |
|
.
The size of the chromosome generally refers to the number of bases, and the chromosomes are numbered roughly in order of size, with one being the biggest. You may also see the unit Mb (megabases or million bases), where 118 Mb = 118,000,000 bases. The chromosomes do "hold their sizes", except for some messy details like Copy Number Variations (insertions and deletions of chunks of DNA) and the fact that we don't have a completely stable reference sequence for the whole genome. But for the purposes of Relative Finder / Family Finder, we can take the chromosomes to be constant in size. To find the size that 23andMe uses for chromosomes, you can go to Family Inheritance / Advanced and compare yourself to yourself.
The cM unit measures the tendency for recombination, which is more important than the number of bases for relationship testing. If you match someone in a region that recombines a lot, that's more impressive than if you match someone where the chromosome seldom splits during recombination.
The number of SNPs depends on how many variant positions have been discovered and how many of those are put on the chip. Some regions have more known SNPs (the HLA region on chromosome 6 is an example), but the cM unit is still the most important. At 23andMe, Version 2 covers about 550,000 SNPs; Version 3 covers closer to 1 million SNPs. Family Tree DNA's new Illumina chip includes a little over 700,000 SNPs in the download file for the autosomes (chromosomes 1-22).
Ann Turner
~~~~***~~~~
CeCe wrote a blog post about investigating your small matches (~5 cMs) on 23andMe, using tools like HIR Search. If interested, go here:
http://www.yourgeneticgenealogist.com/2011/03/investigating-small-segments-of-shared.html
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