As I have mentioned before, cousin marriages were fairly common among my family. My parents are first cousins. So are my father’s parents. My mother’s parents are second cousins once removed. So instead of 32 great-great-great grandparents, I have only about 18.
Since my wife and I are not related, I wondered how my inbred genome had transmitted to our daughter.
Using David Pike’s ROH utility, I computed the regions of homozygosity for my parents, me, my wife, and my daughter, all tested by 23andme.
I used the default settings for the utility. The total Mb gives the total size in megabases of the long autosomal regions where both alleles are the same. The longest ROH gives the size of the longest such region. Percent Homozygous is the percentage of the genome where the two alleles are the same.
I included the worst chromosome column because of my chromosome 9, which is beyond crazy. This column gives the percent homozygosity of the worst chromosome.
| Person | Total Mb | Longest ROH (Mb) | % Homozygous | Worst chromosome (%) |
|---|---|---|---|---|
| Dad | 297.45 | 57.4 | 72.498% | 76.921% |
| Mom | 112.13 | 22.99 | 70.662% | 79.802% |
| Me | 402.78 | 71.38 | 73.588% | 93.542% |
| Wife | 37.33 | 9.64 | 70.003% | 72.411% |
| Daughter | 42.40 | 8.82 | 69.936% | 71.759% |
As you can see, my Dad has higher levels of homozygosity than my Mom as expected and I have the highest levels. My wife is not inbred at all and our daughter has ROH results about the same as my wife. So one generation of marrying someone unrelated, even if from the same/similar ethnicity, has removed all the long runs of homozygosity bred over generations. Good news!
This is much more vigorously seen in animal populations – the introduction of a single outside wolf in an Arctic population, massively changed the health and quality of future generations. But inbreeding in one or two generations doesn’t necessarily produce unhealthy offspring, just like “outbreeding” often produces unhealthy offspring. It’s a probability game, merely decreases the odds of genetic disease. In fact, sex is nature’s way of letting multi-cellular organisms fighting viruses and bacteria….