A North-South Cline: A Northern-African Influence?

Within Europe, HG 21 chromosomes are concentrated in the south (fig. 3E).
Their frequency in the two northern-African samples is very high (52% and 77%), and their frequencies in the Greek and Cypriot samples are also high (~27%), which might reflect a barrier to gene flow between Africa and Europe,
as is also shown by the analysis of autosomal protein markers (Simoni et al. 1999) and microsatellites (Bosch et al. 2000).
In other southern-European populations, such as those in Spain, Portugal, Sardinia, Italy, Turkey, and Yugoslavia, frequencies are in the range of 10%–20%.
The decline in frequencies to the north is rather uniform...