One of many claims without a study attached that I have previously heard was that 53% of the Karaite Jews of Iraq were rhesus negative. I cannot find the actual study at this point, but there is certain data that I do recall.
The study shows a D negative gene frequency of 0.53 and the size of the study was only a little bit more than 100 samples. That small group is likely more or less and extended family, so we need more studies on Karaite communities in order to be able to determine for a fact that Karaite Jews generally speaking have high percentages of rhesus negative blood.
According to the Hardy-Weinberg equilibrium, a 0.53 gene frequency makes the percentage of rhesus negatives among this tested group of Karaite Jews around 28%.
This of course is very high, but less than some claim.
If anyone of you finds the actual study, please drop it in the comment section.