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January 24, 2005

The "fertility inversion"

A week ago a story broke suggesting that a portion of Iceland's population possessed an genetic inversion which conferred upon them possibly greater fertility & lifespan. The authors suggested that this inversion has been selected for in the past 10,000 years and that its separation from the modal type occurred on the order of several million years ago. Additionally, the reports suggested that there was interpopulational differences in the frequency of the inversion.

The supplementary information in the paper did not give explicit frequencies (it presented two diagnostic SNPs in a pie chart from across various populations). I decided to just do a search on ALFRED, and tabulated the exact frequencies of the diagnostic markers as well as the sample size. Additionally, I have included the map with the various ethnic groups so that you can tell which obscure group is where.

The only note I would add is that the "Mixed Europeans" graph is placed on Europe, but when I followed the link, it stated that the sample was "Collected by K. Kidd from unrelated individuals of European ancestry living in the United States and Canada." To reiterate, here is the frequency of the diagnostic markers for the inversion among European groups in the list: Finns (7%), Russians (9-10%), Danes (13-16%), Irish (18-17%), Icelanders (20%) and Mixed Europeans (23-22%). As you can see in the table below, another spike in frequencies seems to be found in populations of Middle Eastern origin (Samaritans, Druze and Ashkenazi Jews, as well as lower frequencies among Yemeni Jews). So, there seems to be two possible components of variation, one radiating out of the Middle East, and another dropping as you move further east in Europe, perhaps a hint of selection after the last Ice Age among the populations that moved north from the Iberian refugia up the Atlantic coast. I can't really think of any obvious reason that "Mixed Europeans" would have a higher frequency than some of the common Northern Europeans. One thought is that Americans are a plural majority of British Isles stock (I tend to think the Census undercounts this group greatly), and we see that in Europe there is an increase of frequency as one moves West. Also, Germans were not sampled, and they are very numerous in the United States. ALFRED does note that "The Irish sample was collected by Prof. K. Kendler and collaborators from people born in Ireland predominantly from the northern and central counties." There is some population substructure in Ireland, so perhaps southern Ireland has higher frequencies of the inversion. Additionally, the high birthrate of the settler colonies might be a factor, as European birthrates might have been more constrained by a ceiling because of resourche limitations, eliminating more of the fertility advantage. Perhaps looking to the Hutterites could provide some evidence in this direction (as they have had very high birthrates for many generations).

Bold indicates markers which are diagnostic for the novel inversion.

Ethnic Group C___7563692_10 A/G C___7563752_10 T/C Sample size C___7563692_10 Sample Size C___7563752_10
Adygei 85% 84% 104 108
  15% 16%    
African Americans 95% 95% 180 178
  5% 5%    
Ami 100% 100% 78 80
         
Atayal 100% 100% 84 84
         
Biaka 98% 98% 134 136
  2% 2%    
Cambodians 100% 100% 50 50
         
Chagga 99% 99% 88 90
  1% 1%    
Cheyenne 97% 96% 104 110
  3% 4%    
Chuvash 90% 90% 82 84
  10% 10%    
Danes 87% 84% 82 102
  13% 16%    
Druze 67% 67% 148 148
  33% 33%    
Europeans, Mixed 77% 78% 174 180
  23% 22%    
Finns 93% 93% 72 70
  7% 7%    
Hakka 100% 100% 78 82
         
Han 99% 99% 98 98
  1% 1%    
Hausa 100% 100% 78 74
         
Ibo 96% 100% 96 94
  4%      
Irish 82% 83% 216 228
  18% 17%    
Japanese 99% 99% 90 94
  1% 1%    
Jews, Ashkenazi 75% 74% 158 162
  25% 26%    
Jews, Ethiopian 98% 98% 60 60
  2% 2%    
Jews, Yemenite 90% 100% 86 86
  10%      
Karitiana 100% 100% 88 108
         
Khanty 96% 92% 100 100
  4% 8%    
Komi-Zyrian 98% 98% 92 94
  2% 2%    
Maya, Yucatan 95% 94% 92 94
  5% 6%    
Mbuti 92% 100% 78 78
  8%      
Melanesia, Nasioi 100% 100% 46 46
         
Micronesians 99% 100% 70 70
  1%      
Pima, Arizona 100% 100% 102 102
         
Pima, Mexico 98% 98% 104 106
  2% 2%    
Russians 91% 90% 96 96
  9% 10%    
Samaritans 63% 64% 82 80
  37% 36%    
Surui 97% 100% 86 94
  3%      
Ticuna 100% 100% 126 130
         
Yakut 98% 98% 102 102
  2% 2%    
Yoruba 100% 100% 156 156

Posted by razib at 01:30 PM