The Doma, also Vadoma or Wadoma (singular Mudoma), are a tribe living in the north of Zimbabwe, especially in the Urungwe and Sipolilo districts on the Zambezi river valley. They have few contacts with the Bantu majority.
A substantial minority of this tribe has a condition known as ectrodactyly in which the middle three toes are absent and the two outer ones are turned in, resulting in the tribe being known as the "two toed" or "ostrich footed" tribe. This is an autosomal dominant condition resulting from a single mutation on chromosome number seven. It is reported that those with the condition are not handicapped and well integrated into the tribe. While possibly an aid in tree climbing the condition prevails because of a small genetic pool among the Vadoma and is propagated by the tribal law that forbids members to marry outside the group.
The Vadoma are a popular example of the genetic effects of small population size on genetic defects and mutation, in a case of blatant inbreeding depression. Due to the Vadoma tribe's isolation, they have developed and maintained ectrodactyly, and due to the comparatively small gene pool, the condition is much more frequent than elsewhere.
The Kalanga of the Kalahari desert also have a number of members with ectrodactyly, and may be related.
Ectrodactyly appears throughout the world. It is caused by various human gene defects. It is also associated with hearing loss. It occurs in 1 out of 90:000 births while limb defects occur in roughly 1 in 1000 births, which by comparison is slightly less than the occurrence of identical twins.
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